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Microbial induced carbonate precipitation (MICP) (also referred to as bio-cementation) is an innovative soil improvement technology, introduced through Bio-mediated Geotechnics. During the process, supplied microorganisms hydrolyze urea, resulting in the formation of calcium carbonate. The precipitates tend to cement the soil particles at particle contacts and enhance the strength of the matrix. Despite the considerable interests in MICP, one major hurdle that hinders the field-scale applications is related to the production of ammonium during the process. The objective of this study is to evaluate the feasibility of struvite (NH4MgPO4·6H2O) precipitation to eliminate the ammonium from the reaction effluent system. For this purpose, the study is considered in two stages: (i) rinsing the ammonium from the sand, and (ii) precipitating ammonium as struvite. In the first-stage, the conditions of rinsing are studied to optimize the removal of ammonium from the soil. In the second-stage, influences of pH conditions, molar ratio and calcium ions on the precipitation of struvite are evaluated. The study demonstrates, through the struvite precipitation technique, around 90% of ammonium could be removed from the effluent. Finding also suggests that the molar ratio (NH4+: Mg2+: PO43-) of 1: 1.2: 1 provides a desirable environment for appropriate removal.

Tellurium is a critical metalloid element that is majorly produced from copper anode slime and is widely consumed in solar energy systems. In this research, a sustainable recovery of tellurium from copper anode slime obtained from Sarcheshmeh Copper Complex, Iran, was investigated. At first, the dissolution of tellurium and other impurities from copper anode slime using sulfuric acid at the atmospheric condition and under pressure in the presence of various oxidants, such as oxygen and hydrogen peroxide was studied. Leaching under pressure using autoclave at 8 bar and 120 °C was concluded as the best leaching route for selective dissolution of tellurium and copper from copper anode slime. The dissolution behavior of the slime impurities was also monitored and considered in the process selection. After the dissolution of tellurium and copper, tellurium precipitation in a form of Cu2Te using cuprous ions was investigated. Complete precipitation of tellurium was attained at 80 °C, using both cuprous ion and metallic copper. The cementation method employed has proven the possibility of tellurium ion reduction solely with the metallic copper. The generated cuprous telluride precipitate was eventually alkaline leached and electroplated from solution on a stainless-steel cathode. This recovery process was designed such that to consume the waste products of the main process with the materials that are produced in a copper refinery plant such as copper chips and electrolyte solution.

Antimonun geleneksel kullanım alanlarının yanında, son senelerde güneş enerjisi teknolojilerindeki gelişmeler antimon ve bileşiklerine duyulan ihtiyacının artması ve birincil kaynakların dünyada hızla tükenmesi ile artan kotalar ikincil kaynaklardan antimon geri kazanımının önemini arttırmıştır. Bu çalışma önerilen geri kazanım yönteminde, daha aktif metalin oksitlenerek iyonik haldeki antimonu indirgemesi ve redüksiyon işlemi sonucu metalik antimonun toz şeklinde üretilmesi amaçlanmaktadır. Cevher ve konsantre içeren oksit ve kükürt esaslı antimon, sırasıyla çeşitli asidik ve bazik çözeltiler ile işlenmiştir. Ancak geri kazanım oranı çok düşük olduğundan, ikincil bir kaynak olan asidik sentetik antimon çözeltilerinden antimonun metalik olarak çöktürülmesine etki eden parametreler detaylı olarak incelenmiştir. Deneysel çalışma şartlarına etki edebilecek sementasyon işlemi sırasında reaksiyon süresi, sıcaklık, başlangıç antimon konsantrasyonu, çinko tozu miktarı ve çözelti pH parametreleri incelenerek elde edilen antimon metalinin fiziksel ve kimyasal özellikleri karakterize edilmiştir. Deneysel çalışmalar sonucunda, 25 ml 1000 ppm Sb+3 sentetik çözeltisi 100 mg metalik çinko ilavesi ile 60 dev./dk. karıştırma hızı ile 5 dakika gibi çok kısa sürede %100’e varan geri kazanım verimine ulaşılmış ve % 99 saflıkta metalik antimon elde edilmiştir. Tek aşamalı sementasyonda 100 mg çinko ile % 100 geri kazanım sağlandığı durumda, iki aşamalı sementasyonda % 40 daha az çinko ilavesi ile aynı verime erişilmiştir.

Cementation or metal displacement reaction is one of the most effective techniques for removing toxic metals from industrial waste solutions. Aims: The main purpose of this work is to study the rate of cementation of cadmium by using a rotating bed of Zn Raschig rings packed in a perforated impeller basket for the investigation of the removal of Cd 2+ from waste solution. Study Design: The reactor was tested for Cd2+ concentration removed, the diameter of Zinc Raschig rings, and the rotational speed of the basket. Methodology: The results indicate that there are two rates of cementation for Cd-Zn system, a high rate at the beginning, followed by a lower rate after the initial period. The results also show that percentage removal of Cd2+ ions from solution increases by increasing the speed of basket rotation, and as the diameter of Zn Raschig ring packed in the basket reactor, increases the removal of Cd2+ decreases. The cadmium deposits on zinc as powder. Results: The removal of Cd2+ is optimum for ring diameter of 0.5 cm, initial concentration of 100 ppm, and basket rotation speed of 500 rpm. The experimental data fit the following equation: Sh=0.041 Sc0.33Re0.40. This equation can be used for the design scale-up and operation of reactors used to remove Cd2+ from wastewater by cementation. Conclusion: Rates of cementation were expressed in terms of the rate of mass transfer, the mass transfer coefficient increases as the rotational speed of the basket increases.

One of the latest developments in biocementation is the use of one-phase-low-pH MICP or EICP method as a more effective and efficient alternative to the traditional two-phase method for the treatment of sandy soil. However, the one-phase-low-pH method has its own limitation. The pH of the solution has to be adjusted before every treatment. In this study, a modified one-phase-low-pH MICP or EICP method is proposed in order to simplify the treatment procedure to improve the efficiency of biotreatment in real constructions. In this method, the low-pH bacteria or urease solution is only used together with the cementation solution (i.e., CaCl2 and urea) for the first treatment and for the subsequent treatment, only cementation solution is used. The test results show that using the modified one-phase-low-pH MICP method with a bacterial solution of a volume ratio of 0.75 is comparable to that using the original one-phase-low-pH method, and 80% of the calcium conversion efficiency can be maintained for up to 5 treatments. However, the modified one-phase-low-pH EICP method may only be used for the first 2 or 3 treatments due to the relatively poor durability of urease enzyme in inducing calcium carbonate during the subsequent injections of cementation solution. Ministry of Education (MOE) Singapore Maritime Institute (SMI) The authors would like to thank the financial supports provided through Grant No. MOE2015-T2-2-142 by the Ministry of Education, Singapore, and the Grant No. SMI-2018-MA02 by the Singapore Maritime Institute which are gratefully acknowledged.

Urease-producing bacteria (UPB) could be used to cement loose sand particles. The UPB would produce free ammonia and carbon dioxide during the process of hydrolyzing urea, and part of the free ammonia would be discharged into the air to cause certain pollution to the atmospheric environment. The carbon dioxide could react with alkaline oxide to form carbonates and improved the strength in GGBS comparing with medium containing different concentrations of urea. By adding hydrogen phosphate ions and magnesium salts, free ammonia could be converted into environmentally friendly magnesium ammonium phosphate. The mixture of biological magnesium ammonium phosphate and basic magnesium carbonate could be synthesized through the bio-mineralization process. Through the pre-precipitation mixing process, the loose sand particles could be cemented into a whole. Scanning electron microscopy (SEM) images of the sand column showed that the mixture of biological magnesium ammonium phosphate and basic magnesium carbonate could better fill in the pores of sand grains. In the pre-precipitation mixing process, the optimal standing time and dosage of the bio-cement slurry prepared by the bio-mineralization method were 6 h and 30%, respectively. The average interface bonding force between CJ2 and glass slide was 2.12 N.

To develop an ultra-high-temperature resistant coating for a reusable thermal protection system, the preparation of a tantalum-based MoSi2-Mo coating by a new two-step process of multi-arc ion plating and halide activated pack cementation is presented. The coating has a dense structure and is well compatible with the tantalum substrate, which can be thermally shocked from room temperature to 1750 °C for 360 cycles without failure. The mechanism of the coating’s excellent resistance to high-temperature thermal shocks is that a strong-binding gradient interface and a dense SiO2 oxide scale with good oxygen resistance are formed by the high-temperature self-diffusion of Si.

Industrial copper slag is among the most important wastes to be evaluated in terms of containing valuable metals and the amount of waste approaching 30 million tons per year. Therefore, in this study, it was aimed to propose a feasible route for copper and zinc recovery from copper converter slag (CCS) by using choline chloride (ChCl) based deep eutectic solvent which is applied on this type of slag for the first time. During the leaching experiments with the pure ChCl-2urea mixture, temperature (25–95 °C), leaching duration (2–72 h), and pulp density (1/10–1/40 g/mL) were selected as the parameters to be investigated for Cu and Zn extraction. After the experimental results, the optimized conditions for the ChCl-2urea leaching process, which gave 89.9% Cu and 65.3% Zn extraction was found at 48 h, 95 °C, 1/20 g/mL pulp density with 600 rpm stirring speed. It is noted that the iron dissolution ratio is very low (max. 4.7%) under the selected conditions. At the end of the iron cementation stage, the total recovery efficiency as a pure metallic copper was 63%. The calculated activation energy for the dissolution of the copper and zinc from CCS is 8.86 kJ mol−1 and 14.48 kJ mol−1, respectively.

This research investigated the treatment process of an Iranian zinc plant residue for recycling lead utilizing brine leaching and cementation with aluminum powder. Response surface modeling was employed for this purpose and accordingly, two quadratic mathematical models with R2 of 0.9058 and 0.9463 were identified for relationship between process parameters. The ANOVA and 3D response surface graphs exhibited that the leaching and cementation processes were significantly depended on the interactive effects between influential parameters. The interaction effects of liquid/solid ratio with NaCl concentration, temperature and stirring rate, and quadratic effect of NaCl concentration had the largest impact on the recovery. It was also distinguished that the most impressive parameters on the cementation performance were the linear effect of Al:Pb molar ratio, cementation time and temperature, and the quadratic impact of agitation rate. Additionally, numerical optimization was carried out by desirability function approach and the maximum leaching recovery of lead (77.14%) was achieved at 400 g/L NaCl concentration, 10 mL/g liquid/solid ratio, 300 rpm stirring speed, 50 °C temperature, and 60-min leaching time. Also, the highest cementation efficiency (74.97%) was determined after 75 min at 1.5 Al:Pb molar (stoichiometry) ratio, ~ 420 rpm agitation rate, and 50 °C temperature. Furthermore, thermodynamic conclusions implied an endothermic nature and good affinity of lead toward each two processes.

Soil improvement techniques have been developed experimentally and empirically from various geotechnical standpoints based on physical, chemical, and biological findings. The traditional microbiological perspectives consider microbially induced soil cementation as an environment-friendly soil improvement technique. In particular, microbially induced carbonate precipitation (MICP) is recognised as an effective method with applications in real geotechnical problems. Traditionally, highly active species with carbonate-precipitating and their optimum environmental conditions have been identified through laboratory experiments and field surveys. Recently, numerical simulations considering microbial metabolic reactions have been tried for elucidating MICP. However, the mathematical and numerical evaluation of the relationship between bacterial growth and MICP requires further investigation. This study proposed a novel numerical simulation scheme for evaluating the effects of bacterial growth on stress distribution in soil micro- and macro-structure. In particular, this scheme utilised a reaction–diffusion system to determine bacterial growth and MICP in micro-structures. Further, stress and strain distributions in multi-scale structures were evaluated by a homogenisation method. Consequently, the simulation results of the calcium carbonate precipitation were 0.85–4.5 μmol/mm3 at 10.3 h. Evidently, the model values are reasonably consistent with the experimental data. Further, the homogenisation simulations indicated that soil stabilisation could be attributed to the formation of a novel skeleton structure comprising soil particles and calcium carbonate-filled soil pores.

This paper presents the hydrometallurgical methods used for the recovery of concentrate and metallic lead from zinc plant residue (ZPR). The ZPR mainly consisting of 9.5% Pb and 7.5% Zn was initially leached by sulfuric acid under the following conditions: leaching temperature 90 °C, leaching time 90 min., sulfuric acid concentration 200 g/l, and solid/liquid ratio 1/5. The zinc recovery obtained was 92.8%, which was finally directed to solvent extraction circuit to produce zinc cathode. Then acidic residue was subjected to alkaline leaching, using sodium hydroxide (NaOH). The lead recovery obtained was 92.58%. For precipitation method by using NaClO, the effects of three important factors including (NaClO/solution) ratio, temperature, and precipitation time were studied and reported. As a result, lead was precipitated in the form of PbO2 with concentrated grade of 72.03% and recovery of 92.31%. Furthermore, aluminum was used for cementation process to produce metallic Pb with grade of 96.11% and total recovery of 87.17%.

Concentration of cementation solution (CCS) is one of the key factors influencing the cementation effect on soil improvement through the microbially induced carbonate precipitation (MICP) process. To precipitate more calcium carbonate per treatment, a higher CCS is needed. However, the MICP process may be retarded or even terminated with an increase in CCS. This retarding effect can be a major limitation for the MICP-based soil treatment and thus needs to be understood properly. This paper presents a systematic study on the conditions causing retarding and its effect on biocementation. The test results of this study have identified that there is retarding effect of CCS on the MICP process, showing that the calcium conversion efficiency, which represents the amount of calcium that has been converted into calcium carbonate in each treatment, reduces with the increase in CCS, and the concentration of calcium is the control factor. The retarding effect will dominate increasingly when CCS is higher than 1.0 M and the amount of calcium carbonate precipitation will reduce for the given amount and type of bacteria used in this study and become zero with CCS of 2.5 M. For the same calcium carbonate content, the unconfined compressive strength is greater for sand treated using a lower CCS as the contribution to the bonding strength by the calcium carbonate generated under a lower CCS is greater than that under a higher CCS. Ministry of Education (MOE) Singapore Maritime Institute (SMI) The authors would like to thank the financial support through Grant No. MOE2015-T2-2-142 provided by the Ministry of Education, Singapore, and Grant No. SMI-2018-MA-02 by the Singapore Maritime Institute. The first two authors would also like to thank the support by the National Natural Science Foundation of China (NSFC) (No. 51708243) and the China Postdoctoral Science Foundation (No. 2018M632862) for the early stage of their research.

To reduce the influence of coating preparation on the mechanical properties of carbon/carbon composites and further improve the antioxidant properties of the coating, a SiC-Si coating was fabricated on carbon/carbon composites by gaseous silicon infiltration (GSI-SiC-Si). For comparison, a SiC-Si coating was also prepared by pack cementation (PC-SiC-Si). A comparative investigation showed the GSI-SiC-Si coating possesses relative lower roughness, better mechanical and anti-oxidation properties. The GSI-SiC-Si coating samples maintained 87.8 % flexural strength of bare C/C composites, while the C/C substrate was severely siliconized in PC-SiC-Si coating samples. The GSI-SiC-Si coating samples could undergo 30 thermal cycles between 1773 K and room temperature and effectively protect C/C composites from oxidation at 1773 K for more than 500 h without weight loss.

Higher manganese silicides (HMS) are promising alternative materials for middle to high temperature thermoelectric applications as a low-cost, non-toxic and highly stable p-type leg. Many of the preparation methods that have been reported previously require long-time and energy consuming processes, as well as expensive equipment, and often do not result in a material of sufficient quality. In this study, the simple, cost-effective and eco-friendly technique of pack cementation is applied. HMS powders synthesized at different experimental conditions are studied and compared considering their structure, composition, short-term thermal stability in air and thermoelectric properties. X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, thermogravimetry and thermoelectric measurements (in terms of Seebeck coefficient, electrical and thermal conductivity) were employed for the characterization of the material and evaluation of its performance. All samples were identified as HMS and only some negligible traces of MnSi were detected. They moderately oxidize when heated non-isothermally under air atmosphere up to 1473 K, while the presence of HMS remains dominant even at such high temperatures. Their thermoelectric properties were remarkable for an undoped material, with a maximum figure of merit (ZT) of 0.47 at 777 K. Pack cementation appeared to have a great potential as the synthesis route of high-efficiency HMS.

To date, more than 600 thousand m3 of liquid radioactive waste has been accumulated at Russian nuclear power plants (NPPs). In addition to radioactive components, they contain a large amount of mineral salts, organic matter, oil products, and suspensions. The problem of overfilling the storage facilities for liquid waste at some NPPs is critical and has to be solved urgently. The article presents modern methods for processing vat residues and the existing prerequisites for modernizing ion-selective purification plants, which are based on the results of research works carried out by various teams. A technological analysis of the methods for evaporation and ion-selective purification of vat residues with identified shortcomings of individual stages of the technologies is carried out. Decontamination of secondary products of liquid radioactive waste processing implies the possibility of subsequently separating valuable components for reusing them. Their decontamination is necessary, since these wastes are essentially high-salt solutions with a specific activity of 106-107 Bq/l contaminated with fission products, radionuclides of corrosion origin, and various substances used to decontaminate the equipment and maintain the water chemistry. It is proposed to apply the electrodialysis method for separating a multicomponent solution of the decontaminated NPP vat residue and to use the obtained products at the plant. Owing to the partial extraction of valuable components from decontaminated vat residues, it becomes possible to reduce the amount of waste and return the separated substances into the main process cycle, thereby reducing the expenditures for initial reagents. To implement the developed technology for component-wise separation of the initial solution, a laboratory electrodialysis facility was manufactured. The project implementation feature was that in dealing with boric acid salts, it is necessary to take into account the danger of their precipitation at certain pH values. It was found that to minimize the escape of boric components, the process should be conducted at low pH values, i.e., the solution should be acidified with the nitric acid obtained in the process. The obtained study results can be used to modernize the cementation plants.

In the present study, the interactive effects of the process variables containing copper concentration, temperature, and time on the efficiency of copper cementation by metallic aluminum particles were examined by using response surface methodology (RSM). It was observed that the efficiency of cementation increased with an increase in the initial concentration of copper, temperature and time. The multiple regression analysis to the experimental data was applied to see the interactive effects of process variables. The second-order polynomial equation was obtained. The optimal values were found to be 0.075 mol/l, 303 K, and 90 min to maximize the amount of the deposited copper.

Methods of binary and ternary powdery alloys (Cu-Sn, Cu-Zn, Ni-Cu-Zn, Ni-Sn-Zn, Cu-Fe, Ni-Cu-Fe, Ni-Cu, Ni-Cu-Al) preparation with core-shell particles structure have been developed using the processes either of copper, nickel, tin ions cementation from solutions with tin, zinc, iron powders or nickel chemical deposition from hypophosphite solutions on the mixtures of copper and aluminum powders. Metals quota in the powdery products can be controlled by varying the duration of cementation or chemical deposition, the ratio of reagents quantities, pH and concentration of solutions. The possibility of simultaneous reduction of nickel(II) and tin(II) ions with zinc powder or copper(II) and nickel(II) ions with iron powder with the formation of ternary alloys has been revealed. Low-temperature formation of intermetallic phases in Cu-Sn, Ni-Sn-Zn systems and solid solutions in Ni-Cu-Zn, Cu-Fe, Ni-Cu-Fe systems has been shown to occur during the cementation. The particles of the initial powders (Al, Cu) are coated with loose and more or less sealed shells during nickel chemical reduction from solutions. Spherical particles, flower-type compact aggregates or dendrites, depending on the nature of metals and processes duration, are formed during the cementation. The powders obtained by cementation andchemical deposition from solutions can be used in the manufacture of products for structural and instrumental (Cu-Sn, Cu-Zn, Ni-Cu-Zn, Ni-Sn-Zn, Cu-Fe, Ni-Cu, Ni-Cu-Al), antifriction (Ni-Cu-Fe, Ni-Cu) and electrical (Ni-Cu, Ni-Cu-Zn) applications, as well as solders (Cu-Zn, Ni-Sn-Zn).

In this research, SiC coating was applied by pack cementation method at 1600°C to protect graphite and three-dimensional (3D) C/C composite from high temperature oxidation. The powder pack consiste...

Purification of molten salt is essential for producing highly pure metal from melts by chemical reactions and electrolysis. Cementation is a technique used for refining molten ZnCl2-based salt. In this study, we investigated the thermodynamics involved in the reduction of CdCl2 in molten ZnCl2-based salt with Zn metal to optimize the separation conditions for Cd; this is difficult as both Cd and Zn have similar electrochemical potentials. We experimentally investigated the thermodynamic equilibrium between the molten ZnCl2-based salt and liquid Zn–Cd alloy at 723 K (450 °C). The equilibrium concentration of CdCl2 in 40 mol pct ZnCl2-NaCl-KCl coexisting with Zn-Cd alloy changed as the ratio of NaCl and KCl was altered. The activity coefficient of CdCl2 in the system at 723 K (450 °C) was obtained with the calculated activity coefficient of ZnCl2 using several thermodynamic solution models. A two-step cementation process was used to demonstrate the possibility of lowering the concentration of Cd. The Cd content in molten salt was lowered to ~ 10 mass ppm by the two-step reaction, and the feasibility of multi-step cementation was demonstrated.

Abstract Insufficient recycling of a continuously increasing amount of liquid crystal display (LCD) waste leads to the waste of potentially recyclable materials, especially rare and critical indium. Moreover, landfilling of LCD waste increases the potential for environmental risk. This paper describes a recycling process combining membrane filtration unit processes to hydrometallurgical indium recovery process. The LCD panels were crushed and leached with 1 M H2SO4. 97.4% yields on average were obtained, and a novel finding was made about fast kinetics (2 min for the maximum indium yield). Ultrafiltration was used to remove the dissolved organic material from the leachate, which was concentrated with nanofiltration before liquid–liquid extraction for indium purification. The results showed that commercial polymeric membranes removed more than 90% (from over 3000 mg/L to under 200 mg/L) of the dissolved organic compounds, thus potentially significantly diminishing the detriments caused by these compounds in the liquid–liquid extraction step. The concentration of the leachate with nanofiltration enables the use of smaller processing equipment and to save chemicals in the further steps of the process. The indium content in the leachate was more than five times higher after nanofiltration than after leaching (126 mg/L vs. 677 mg/L). In liquid–liquid extraction, the phase separation took place in only 34 s with the membrane-treated leachate, while with the untreated leachate it remained incomplete even after three hours. The purity of indium was increased from 10 to 74%. From the obtained HCl solution, a 95.5% pure indium product with 69.3% yield was obtained by cementation. Graphical Abstract

As a category of crucial wear-resistant alloys, high-chromium cast irons (HCCIs) are widely used in mining, minerals and cementation industries. The large volume fraction of coarse primary M7C3 carbides (PC) imparts excellent wear resistance. However, coarse carbides also induce brittleness, resulting in high cracking susceptibility, and early failure of components, particularly under impact. To minimize the brittleness and increase the service life of HCCI parts, different techniques have been developed through modifying the carbide morphology and refining its size. This paper comprehensively reviews the currently available methods that have either been used in industry production or in laboratory development to modify the primary M7C3 carbides in various HCCIs. The possible mechanisms that govern the refinement of primary carbides are also discussed in-depth. Based on previously published work, the mechanical performance of HCCIs is correlated with the microstructure of the matrix, and with the size, shape, volume fraction and distribution of primary carbides. This may provide solid fundamental to develop more effective techniques and/or new alloys to further improve the properties of this type of materials, increasing their engineering service life and to tailor their wider applications. In addition, the present work also seeks theoretical feasibility to apply the recently well-established theories/models of grain refinement for cast metals to refinement of the primary carbides in HCCIs.

Gold cementation kinetic features from cyanide solutions using zinc powders of various origins were studied. The first powder was obtained by distillation and is currently used in the vast majority of industries (traditional powder). The second powder was obtained by electrochemical reduction from alkaline solution (electrolytic powder). The main distinguishing feature of these powders is specific surface area. This indicator for the electrolytic powder is 2.6 times higher than for the traditional one (3.02 and 1.16 m2/g, respectively), which is associated with dendritic form of electrolytic powder. For cementation studies, a solution with a gold content of 50.8 μmol/dm3 and 0.04 mol/dm3 sodium cyanide (NaCN) was taken. Studies have shown the presence of a depassivation period associated with oxide film dissolution on the powder surface and overcoming diffusion difficulties. The depassivation period of a traditional powder (10–15 seconds) exceeds the depassivation period of an electrolytic powder (5–8 seconds). Values of cementation reaction experimental rate constants are determined for the process using traditional and electrolytic powders at different ratios of zinc and gold masses in solution. Experimental reaction rate constants for electrolytic powder under the studied conditions are 1.3–1.6 times higher than the experimental rate constants for traditional powder. Zinc oxidation rates are compared under these conditions for various ratios m(Zn)/m(Au). Powder dissolution rates referred to specific surface area (taken in initial period) practically do not differ. The electrolytic powder’s absolute dissolution rate at the initial time is almost two times greater. As powder reacts with an alkaline solution, absolute dissolution rates of electrolytic and traditional powders are equalized.

This article is devoted to the influence of sodium lignosulfonate (SL), anionic surfactants (sodium dodecylsulfate (SDS), sodium dodecylbenzene sulfonate (SDBS)), and their mixtures on the copper cementation rate by zinc. The results demonstrated a copper cementation rate decreasing at LS and SDBS concentrations increasing. Excessive zinc consumption was also detected on copper-ion cementation due to LS and SDBS anion adsorption onto positively charged zinc cathodic areas and copper particles. This led to a decrease in the growth rate of nuclei of copper particles and energy consumption for the formation of new nucleation centers, as well as the creation of conditions for reducing the overvoltage of hydrogen evolution. At the same time, an increase in temperature led to zinc consumption decreasing in the presence of LS. The reagents under investigation could be ranked according to their degree of negative influence on copper cementation increasing in the following order: SDS < SDBS < LS. Testing LS and SDS mixtures showed their irregular influence on the copper cementation rate at different temperatures. In experiments with LS and SDBS mixtures, a linear decrease in the copper-ion cementation rate upon an increase in SDBS concentration and simultaneous zinc-consumption enhancement was fixed. Due to the negative influence of the investigated reagents, we offered a purification method from organic impurities through the use of multilayered alumosilicates modified by cationic surfactants. The results indicate the high effectiveness of removing organic impurities from solutions, which allowed us to increase the cementation rate in the presence of the LS and SDBS mixture by 50% while, at the same time, decreasing zinc consumption. © 2020, Allerton Press, Inc. This work was supported by the Russian Foundation for Basic Research as part of scientific project no. 18-38-00388.

Minor additions of reactive elements (Y, Ce, La, Zr, Hf, etc.) significantly affect the high-temperature oxidation behavior of protective oxide scales. Designing oxidation-resistant aluminide coatings having optimum content of reactive elements is challenging due to the observed hindering effect of these elements on the coating formation. In the current investigation, this effect has been studied by examination of a high activity aluminide coating in powder mixtures of Al, NH4Cl, Y2O3, and Al2O3 with different Y2O3 contents. Oxides of Zr, Ce, and La were also examined for comparison. Cross-sectional microstructure of coatings and weight changes of the specimens were studied at different aluminizing times. The results showed that the inhibition effect applied for all reactive elements under investigation with different strengths and intensifies with more additions of Y2O3 up to a saturation limit. The observed inhibition effect was explained based on the equilibrium amounts of gaseous halides responsible for transfer of coating elements. It was demonstrated that the addition of Y2O3 can decrease the amount of aluminum carrier halide significantly. The mechanism of inhibition was attributed to the large agglomerates rich in aluminum and reactive elements detected in the pack after aluminizing treatment.

The study covers kinetic features of gold cementation from cyanide solutions using two zinc powders of various origins. The first one was obtained by distillation and is currently applied in gold cementation from cyanide solutions (traditional powder). The second one was obtained by electrochemical reduction from the alkaline solution (experimental, electrolytic powder). The main distinguishing feature of these cementation powders is their specific surface area. This indicator for the electrolytic powder is 2.6 times higher than for the traditional one (3.02 m2/g and 1.16 m2/g, respectively) due to its dendritic form. The studies used a solution with a gold content of 50.8 μmol/dm3and a sodium cyanide content of 0.04 mol/dm3NaCN was taken. Cementation revealed a powder depassivation period associated with oxide film dissolution and overcoming diffusion difficulties. The traditional powder depassivation period (10–15 sec) exceeds that of the electrolytic powder (5–8 sec). Experimental rate constants of the cementation reaction were determined for the process involving both powders under study at different ratios of zinc and gold masses in the solution. Experimental reaction rate constants for the electrolytic powder under the studied conditions were 1.3– 1.6 times higher than that for the traditional powder. It was found that oxidation rates of zinc powders compared at different ratios of zinc and gold masses are virtually the same. At the same time, absolute rates of electrolytic powder dissolution in the initial period are nearly 2 times greater. As the powder reacts with the alkaline solution, absolute dissolution rates of electrolytic and traditional powders are equalized.

The article focuses on the effect of sodium lignosulfonate (LS), anionic surfactants (sodium dodecylsulfate (SDS), sodium dodecylbenzene sulfonate (SDBS)), and their mixtures on the rate of copper cementation by zinc. The results obtained demonstrate a decrease in copper cementation rate with the increasing LS and SDBS concentrations. There was also excessive zinc consumption for copper ion cementation noted due to LS and SDBS anion adsorption on positively charged zinc cathodic areas of the cementing agent and the precipitate. This led to a decrease in the rate of copper particle nucleation, energy consumption for forming new copper nucleation centers, and conditions for hydrogen overpotential reduction. In addition, rising temperature led to a decrease in zinc consumption in the presence of LS. Surfactants under investigation may be ranked by the negative impact on copper ion cementation in an ascending order as follows: SDS < SDBS < LS. LS + SDS mixture testing showed its irregular effect on copper cementation rate at test temperatures. Experiments with LS and SDBS mixtures demonstrated a linear decrease in copper ion cementation rate with increasing SDBS concentration and simultaneously rising zinc consumption. Due to the negative impact of investigated reagents discovered, we proposed a method for removing organic impurities from solutions using multilayered aluminosilicates modified by cationic surfactants. The results obtained indicate the high effectiveness of organic impurity removal from solutions providing for a 50 % increase in cementation rate in the presence of LS + SDBS mixture together with a decrease in zinc consumption.

Silver recovery from a spent submarine battery was investigated. The effect of different parameters including nitric acid concentration, temperature, solid to liquid ratio (w/v%) and time was studi...

The present study is concerned with the removal rate of Copper ions Cu++ from wastewater by cementation of copper from copper sulfate solution on a horizontal steel sheet placed at the bottom of a square stirred tank reactor and fitted with square steel turbulence promoters. The variables studied were solution concentration, rotation speed, impeller geometry, promoter diameter and distance between promoters. The rate of mass transfer was found to increase with the rotational speed and decreased with the increase of distance between promoters. The data were correlated to develop the relationship Sh α Re x

Tantalum (Ta) alloys are important ultra-high-temperature structural materials owing to their excellent high-temperature mechanical properties and processability. However, they exhibit poor high-temperature oxidation resistance. In this study, a dense MoSi2 ceramic coating was prepared on a Ta substrate using an innovative multi-arc ion plating process and halide activated pack cementation in order to improve its ultra-high-temperature oxidation resistance. This ceramic coating exhibited a low roughness space arithmetic (287.1 ± 26.3 nm) and a dense structure. The relationship between the thickness of the coating and the duration of pack-cementation at 1250 ℃ was parabolic. The coating had a service life of more than 12 h at 1750 ℃, and showed excellent high-temperature oxidation resistance because of the uniform and dense structure of the coating and the rapid formation of a dense SiO2 layer with low O2 permeability during high-temperature oxidation.

Steel substrates low carbons were face-hardened by cementing in case, and then thin layers of chromium were deposited by electrolytic way on these substrates. After deposition, the samples were exposed to isothermal annealing in the temperature of 950°C. The characterization of the thin layers was made by means of optical microscopy and interferometry Vickers micro-hardness. From the obtained results, we have established the kinetics of phase shift (under effect the layer of cementing) in the thin layers of chromium which are transformed into chromium carbide while passing by metastable phases of transition. These transformations occurred by diffusion of the carbon atoms coming from layer of cementing, germination and growth in solid phase. This fact has examined according to the temperature of annealing, the evolution of the lattice parameter and the morphology of the deposited chromium layer. As regards the mechanical properties, it was established that the micro-hardness believes with the evolution of the phase shift.

Copper smelting open-circuit (CSO) dust contains various valuable metals, such as copper, lead, and zinc, as well as undesirable toxic elements such as arsenic. Thus, the comprehensive recovery of valuable elements from CSO dust is highly significant from both economic and environmental perspectives. In this review, pyrometallurgical, pyrohydrometallurgical and hydrometallurgical processes are evaluated after the presentation of the formation mechanism and characterization of CSO dust. Hydrometallurgical processing is more suitable for treating the dust because of its low energy consumption, high metal recovery, and no secondary pollution. After the introduction of valuable metal recovery by cementation, sulfuration precipitation, and solvent extraction from CSO dust leaching solution, arsenic removal from the solution by lime, sulfides, iron salts, and natroalunite precipitations was reviewed. Arsenical natroalunite has excellent long-term stability, so natroalunite precipitation is very promising for arsenic immobilization.

Hydrogen peroxide (H2O2) is a commonly used chemical agent in orthopaedic practice for antisepsis, haemostasis and preparation of bone bed for cementation. However, the associated risks of H2O2usage are not widely known. We report a case of suspected air embolism after use of H2O2during drainage of a septic arthritis of the shoulder.Upon our literature review, we were able to demonstrate H2O2to be beneficial in antisepsis and care of chronic wounds. However, it has not been proven to be superior to other antiseptics commonly used in orthopaedic surgery. Regarding its use in cementation, there is evidence to show it is more effective than saline however, the use of pulsatile lavage appears to be the most important factor affecting the quality of cementation. H2O2has not been shown to be helpful with haemostasis. Prior to the use of H2O2, one should be cautious and understand its associated risks and precautions.

In present article gold cementation features from cyanide solutions using dendritic zinc powders are studied. The powders were obtained by electroextraction from alkaline solutions. Powders with different physical properties were obtained by means of change in current density (from 0.5 to 2 A/m2) and NaOH concentration in solution (from 100 to 400 g/dm3) at the constant zinc concentration (10 g/dm3). The physical properties of mentioned powders were studied using SEM (Jeol JSM-6390LA), BET (Gemini VII 2390) and laser diffraction (Sympatec HELOS & RODOS). It is shown that electrolytic powders have high specific surface area, which is 1.8–2.6 times larger than the surface area of ​​the zinc powder currently used for cementation. At that electrolytic powders particle size is 8-22 times larger than the particle size of powder currently used for cementation. The reason of high specific surface area is the electrolytic zinc powders dendritic structure. It was found that the obtained powders precipitate gold from cyanide solutions with a greater efficiency in a wide range of productivity. Laboratory unit simulating Merrill-Crow technology was used for cementation. Immediately ahead conducting the experiments, Na2SO3 was added to the solution in excess to remove dissolved oxygen. Zinc powders were plated by dendritic lead before loading into the laboratory setup by cementation. Lead was added as acetate (Pb (CH3COO)2). The consumption of lead acetate was 10% by weight of zinc. Correlation between the powders physical properties and the gold extraction is shown.

The studies on cementation focus exclusively on the carbon’s movement. It is described by diffusion equations, often with constant coefficients and without regard to the liaising with temperature. It does not allow to have regard to the further carbon diffusion into the workpiece with the lower temperature range. The most accurate prediction of carbon concentration profiles depending on the parameters of the carburization regime and the chemical composition of steel is possible with the mathematical models using. However, most models show good results for Fe-C austenite without affecting the effect of alloying substitution elements. Taking into account the influence of alloying elements leads to complex empirical dependencies with difficult selected coefficients. It makes their use difficult. The study describes the simulation using the finite element method for the process of austenite’s diffusion saturation Fe-C-Cr system with carbon during cementation. Here is an example of a steel gear 15Cr2 with the temperature influence. The COMSOL Multiphysics program is used to solve the problem numerically. It is found that the model of carbon diffusion in unalloyed austenite for the single-stage cementation regime is in good contact with the experimental data for the Fe-C-Cr austenite of 15Cr2 steel. For a two-stage process, the calculation of the carbon concentration in the surface layer has a slightly greater deviation from the experimental data than it is at a greater depth.

It was studied diffusive mobility of carbon’s atoms in the process of decarbonation steel У8 and cementation steel Ст3 in the temperature’s interval of polymorphic transformation. It was set that low temperature cementation (LTC) is possible only after a preliminary austenitization steel. In the state of polymorphic transformation due to the weakening of interatomic interaction, the formation of a two-phase structure of complexes, there is a decrease in the activation energy of carbon diffusion and a corresponding increase in the diffusion coefficient, which indicates the possibility of conducting LTC. The diffusion ability of carbon in LTC in a two-phase state was estimated using the value of the effective activation energy of diffusion taking into account the relative content of austenite and ferrite according to the «lever» rule. As a result of the studies performed, the following two-stage LTC method is proposed: the first stage – austenization (carburization) of the surface layer at a temperature of 920 °С for 20 minutes; the second stage – cementation in the temperature range 700…740 °С for 2 hours. Subsequent hardening and low-temperature tempering provide the required quality of the cemented layer by analogy with the traditional cementation process.

This work is devoted to research of the structural-phase condition and changes in the mechano-tribological properties of 0.3C-1Cr-1Mn-1Si-Fe structural steel after plasma electrolytic cementation. Using metallographic and X-ray analysis, mechano-tribological tests, it was found that 0.3C-1Cr-1Mn-1Si-Fe steel in the initial state belongs to the ferritic-pearlitic class, which contains ~ 65% of pearlite grain and 35% of ferrite grain. When samples of 30HGSA steel are saturated with carbon, a modified surface layer with a thickness of 25μm is formed on the surface of the studied samples, including α-Fe ferrite, cementite Fe3C, iron Fe3C2carbide and an alloying element. It was established that the intensity of wear of the samples after modifying decreased by 2 times, and the surface microhardness after cementation increased 3 times, depending on the original sample.

The subject of study was the Safyanovskaya Med company’s acidic underspoil water containing 0.17 g/liter of copper and 1.8 g/liter of zinc (pH 2.8–2.9). The goal was to study and develop a technology of cleaning water of impurities (copper, zinc, aluminum, iron, manganese), accompanied by extraction of copper and zinc in the form of commercial products. Copper extraction by cementation with metallic iron was studied. It was shown that this method could allow extracting 94–95% copper into a concentrate. The role of resolution processes of precipitated copper in cementation was established. To reduce the consumption of iron and to improve the quality of precipitated copper, it is proposed to carry out cementation in a washbox. The copper content in the concentrate was 27–28%, while the specific consumption of iron was 7.0–7.5 kg/kg of copper. During the studies of material composition of copper precipitate, the formation of cuprospinel, goethite, and bassanite phases and the precipitation of basic aluminum sulfates were detected. The extraction of zinc from the solution after copper removal was studied by precipitation with sodium sulfide. As a result, a concentrate was obtained with a zinc content of 49.6–50.9% with extraction of 99%. The process regularities for zinc concentrate dehydration were studied. By optimizing the crystallization conditions of the precipitate, a minimum final cake moisture content of 40–42% was reached. A process flow diagram for acidic underspoil water, including copper cementation and the precipitation of zinc sulfide, was developed. According to this diagram, the mother solution from zinc precipitation should be treated with lime until the pH reaches 10–10.5, followed by slurry settling. As a result, clean water of the following composition is obtained, mg/liter: 0.05 zinc, 0.01 copper, 0.02 aluminum, < 0.02 iron, 0.05 manganese. These values correspond to the quality of drinking water according to GOST R 51232-98.

The subject of interest in this study was lead cementation with zinc from solution after conventional agitate acidic leaching of converter dust from secondary copper production. The kinetics of lead cementation from an acid solution of lead acetate using zinc powder was studied. The optimal cementation conditions for removing lead from the solution were determined to have a stirring intensity of 300 rpm, a zinc particle size distribution mm and an ambient temperature. Under these conditions, an almost 90% efficiency in removing lead from solution was achieved. The cementation precipitate contains Pb, and a certain amount of Cu. Lead is present in the cementation precipitate in the PbO, Pb5O8 and Pb(Cu2O2) phases. The solution after cementation was also refined from copper. The solution can be used for further processing in order to obtain a marketable Zn-based product. The resulting cementation precipitate can be further processed and modified to obtain a lead-based product. A kinetic study of the process of lead cementation from solution was also carried out. Based on experimental measurements, the value of apparent activation energy (Ea) which was found to be ~18.66 kJ·mol−1, indicates that this process is diffusion controlled in the temperature range 293–333 K.

Lead (Pb) contaminated soils pose serious risks to human health and the environment. One remediation technique that permanently removes Pb is chemical soil washing. This study investigated a modified chemical soil washing technique whereby Pb extraction in citrate solution and recovery of dissolved Pb by reductive precipitation (cementation) were simultaneously carried out in a single reactor by the addition of micro-sized zero-valent iron (mZVI) to decontaminate Pb-contaminated soil from a shooting range. Pb-loaded mZVI were then recovered by magnetic separation. The effects of mZVI dosage, citrate concentration, pH, and hydrodynamics on Pb removal were evaluated. Under acidic pH, Pb removal increased with increasing citrate concentration. The addition of mZVI suppressed Pb removal from 59.6 to 30% in 0.1 M citrate solution, which was attributed to dissolved Fe ions competing for free citrate ions to form soluble Fe-citrate complexes. Increasing the citrate concentration and shaking speed enhanced Pb extraction from the soil and subsequent recovery via cementation onto mZVI. Pb removal and recovery onto mZVI of up to 99.0% were achieved at citrate concentration of 0.7 M, pH of 5, and shaking speed of 165 strokes/min. The addition of mZVI during chemical soil washing in citrate solution not only extracted and recovered Pb from the contaminated soil but also eliminated the need to wash soil residues obtained after treatment because the bulk of dissolved Pb was sequestered from the solution.

Since the accident at the Fukushima Nuclear Power Station, the stabilization of radioactive nuclides such as alkali metals like Cs has become very important. Cementation is a widespread technique f...

The study covers physicochemical features of dendritic zinc powders and their effect on gold cementation from cyanide solutions. Three zinc powders were obtained in a laboratory environment by electroextraction at different conditions, and these powders featured various particle size and specific surface area. The properties of zinc powders obtained and powder currently used for gold cementation were evaluated using SEM (Jeol JSM-6390LA), BET (Gemini VII 2390) and laser diffraction (Sympatec HELOS & RODOS) methods. It is shown that electrolytic powders have high specific surface area (1.3–2.6 times more) and a low bulk density (3.1–3.8 times less), relative to zinc powder currently used for gold cementation. It was found that due to specific physical properties electrolytic powders have low hydraulic resistance, which eliminates the need for inert additives introduced during cementation, increases unit capacity and reduces the load on equipment. Inert additives elimination will additionally increase the gold content in the resulting product. The dendritic morfology of zinc powders obtained compensates high particle size resulting in the high efficiency of gold precipitation. At the long cementation cycle the effective gold deposition area (with gold extraction of more than 97 %) turned out to be shorter for electrolytic powder compared to fine powder currently used. However, in practice, the cementation cycle is always limited by fine powder throughput and it is not possible to achieve the full zinc potential. The resulting cementation product usually contains 25–35 % of unused zinc. These studies show the effectiveness of using electrolytic zinc powder for gold cementation from cyanide solutions.

The performance of a rotating fixed bed reactor in recovering copper from industrial waste solutions by cementation is studied under various conditions. The rotating fixed bed is made of stacked woven steel screens to take advantage of two features of screens: the ability to present large area per unit volume and their ability to promote high turbulence. Variables studied are initial CuSO4 concentration, bed rotation speed, mesh number of the screens and bed thickness. The presence of baffles was found to increase the rate of cementation. The data were correlated by a dimensionless mass transfer correlation suitable for the design and operation of large scale cementation reactors.

Globally, continuous R & D efforts are being made to recuperate precious metals from wastes in order to conserve the natural resources as well as minimize environmental pollution. Keeping in view of the above, a process has been developed to recover gold from industrial effluent using hydrometallurgical route. Initially, the effluent was pre-treated using precipitation and solvent extraction techniques to remove impurities, i.e., iron and copper as value added products. Iron was removed up to 99.99% at pH ~ 3.5. Further, copper was extracted using 10% LIX 84IC maintaining phase ratio 1/1 in mixing time of 15 min and equilibrium (eq.). pH 2.2. Selective adsorption of gold was carried out using ionenaustauscher-II and resulted in 99% gold adsorption between pH 7 and 8 in contact time of 30 min. Experimental results obtained for the adsorption of gold was found to follow second order reaction and fitted well with the Freundlich isotherm. Gold from the loaded resin was eluted using a mixture of hydrochloric acid and thiourea. From the pure gold solution, metal could be produced using cementation/charcoal adsorption followed by heat treatment, respectively.

The author studied the process of copper removal from underspoil water at Blyavinskoe and Safyanovskoe copper ore deposits by cementation by iron. The influence of pH, consumption of cementation agent impurity ions Fe3+, Al3+ and Ca2+, as well as timing on the cementation performance was analyzed. The mechanism of the process was determined, and by-reactions resulting in over-consumption of cementation agent were revealed. The studies of the material constitution of cemented copper showed that the concentrate quality worsened because of the joint settling of basic aluminum and calcium sulfates. The obtained results make it possible to draw the conclusion on applicability of cementation for removal of copper from underspoil water.

Stainless steel can be applied as interconnect materials in solid oxide fuel cells (SOFCs) at operating temperatures 600–800 °C. Chromium (Cr)-forming stainless steel as an interconnect plate possesses a low oxidation resistance at high temperature and electrical conductivity, and volatility of Cr oxide scale can poison the cathode material. One effective strategy is to use a surface coating to improve interconnect performance. This work is to form cobalt (Co)-containing coatings on the surface of AISI 430 ferritic stainless steel interconnect via pack cementation approach. The resultant coating is extremely effective at heightening the oxidation resistance and electrical conductivity of AISI 430 ferritic stainless steel. The area specific resistance of samples was measured as a function of time. The area specific resistance of coated sample with 2% of activator content and holding time of 2 h is 90.21 and 108.32 mΩ cm2 after 450 h of oxidation in air, respectively. Additionally, the coated sample with 2% of activator content and holding time of 2 h has a weight change of merely 0.299 and 0.231 mg/cm2 after 650 h of isothermal oxidation at 800 °C, separately. The results displayed that the formation of CoFe2O4 spinel coating enhanced oxidation resistance by inhibiting the outward diffusion of Cr cations and the inward diffusion of oxygen anions.

In this study, we tried to improve the oxidation resistance of Mo–3Si–1B (wt%) alloy at intermediate (800 °C) and high temperature (1300 °C) after applying Si/Al pack cementation coatings. In addition, we examined structural changes and phase change in the intermediate and high temperature oxidizing atmospheres to observe oxidation behaviors. The diffusion pack coatings were carried out with an NH4F activator and both Si and Al powder mixtures. Mo–Si–B alloys were subjected to diffusion coatings of Si/Al powders at various temperatures in various time conditions at a temperature of 1100 °C. When the pack coatings were carried out for 48 h, Mo(Si, Al)2 and Mo3Al8 layers together with a T2 (Mo5SiB2) layer were successfully synthesized on the substrate. After oxidation tests, an Al2O3 protective oxide layer was formed by the diffusion of Al in an ambient atmosphere. The Si/Al pack cementation coatings provided excellent oxidation resistance through the formation of an Al2O3 oxide layer. The enhanced oxidation behaviors are discussed in terms of microstructural evolution at high temperatures.

Free oxides in soils usually have distinct electrochemical properties, generate both CEC and AEC as a consequence of the adsorption of proton and hydroxyl ions provide structural cementation in the...

Due to the wide applications, limited supply, and high demand, sustainable utilization of indium has become an important task. In this study, the recovery of indium from acidic extractant solutions of ITO scraps using aluminum (Al) powder was investigated. The cementation reaction of indium from HCl solution was completed within 10 min and it could be described by pseudo-first-order kinetic model. Effective recovery of indium (91.69%) at aluminum dose of 5 g/L and 25 °C was found in HCl solution. Recovery efficiency increased with aluminum dose. Results from cyclic voltammetry were used to provide information why cementation reactions did not work in H2SO4 or HNO3 solutions. Indium recovery by aluminum cementation could be an alternative process, which is simple and efficient. However, there are some drawbacks, e.g., cementation reaction was not specific as tin was recovered simultaneously with indium from solutions. Furthermore, removal and separation of indium deposit on aluminum surfaces could be another issue.