Search

The valorization of slag from the production of high-carbon ferrochrome is a challenge for ferrochrome producers. The recycling of high-carbon ferrochrome slag was explored through the smelting route to recover Fe–Si–Al–Cr alloys and reengineer the residual slag for alumina-enriched refractory material. In this research, the focus was to reduce the SiO2% and enrichment of Al2O3% in the final slag and recover the metallic value in the form of a complex alloy containing Fe, Si, Cr and Al. The manuscript consists of a thermochemical simulation of the smelting of FeCr slag followed by smelting experiments to optimize the process parameters such as temperature and the addition of coke, cast iron and alumina. An experimental investigation revealed that the maximum recovery of Si (57.4% recovery), Al in the alloy (20.56% recovery) and Al2O3 (85.78% recovery) in the slag was achieved at a charge mix consisting of 1000 g of FeCr slag, 300 g of alumina, 200 g of cast iron and 300 g of coke. The present study also demonstrated the usefulness of prior thermochemical calculations for smelting metallurgical wastes such as slag from high-carbon ferrochrome production for value creation and reutilization purposes. [ABSTRACT FROM AUTHOR]

Reactive powder concrete (RPC) is a new generation concrete with high strength, used in special structures, and its use is increasing day by day. In this study, instead of using high-strength aggregates typically used in RPC, wastes released in ferrochrome production were used. In addition, the possibility of using fibers obtained from end-of-life automobile tires (ELT), instead of the micro steel fibers typically used in RPC, was investigated. Thus, sustainable green reactive powder concrete (GRPC), the material which is obtained from waste materials except the binder and chemical additive, has been developed. As ferrochrome wastes, olivine, serpentine, rum, slag, and pure waste were used as powder and aggregate in GRPC. Firstly, in GRPC without fiber, the physical and mechanical properties of ferrochrome wastes were examined by using different ratios. Then, the optimum mixture was selected, and different ratios of industrial steel and ELT fiber were added to this mixture. As a result, the compressive strength of GRPC using olivine and pure waste (ferrochrome slag) is close to the reference RPC. However, it is 28% more economical. The flexural strength of the samples with a 4% addition of industrial or ELT fiber increased by 182% and 213%, respectively, compared to the reference sample without fiber. With the use of 4% ELT fiber (by volume) in GRPC, the flexural strength increased by 11% compared to the use of industrial steel fiber. In terms of cost, with the use of ferrochrome waste and ELT fiber, GRPC was 48% more economical. When examined in terms of the flexural and compressive unit strength cost, GRPC was approximately 41% more economical. As a result of this study, high-performance concrete with high mechanical properties that is economical, sustainable, and environmentally friendly has been produced by evaluating the use of waste materials. [ABSTRACT FROM AUTHOR]

There is limited data on studies that have focused on the kinetics, thermodynamics, and characterization of struvite crystallization from alternative magnesium sources. This study focused on thermal analysis of struvite (produced using ferrochrome slag as a magnesium source) and the results indicated that the residual quantities of struvite were lower than the theoretical mass loss of struvite of 51.42%. When using ferrochrome slag (FCS) as the magnesium source, 47.9%, 47.4%, and 46.9% losses in mass were observed for heating rates of 5°C/min; 10°C/min and 15°C/min respectively. The mean activation energies for struvite produced using FCS were deduced using isoconversional kinetic methods and ranged from 49.81to 56.20 kJ/mol which is very similar to the activation energies deduced using MgCl2. The study also focused on the surface morphology, and particle size of the final product at different pH and N:P ratios. The final particle size distribution of the product was significantly influenced by the solution pH. To improve the crystal growth kinetics for both MgCl2 and FCS, a high ratio of N:P molar ratios should be adopted. The product's highest median particle size was obtained using FCS as the magnesium source at a low pH. Median particle size increased with decrease in pH, at a pH of 7.5 the recorded median particle size was 96 µm whilst, the lowest was 31 µm at a pH of 9.5. The highest percent of fines (

Ferrochrome slag (FS) contains a large number of glass phase, which cannot be effectively transformed into crystalline phases during the reutilization for fabricating ceramic materials. In this study, cordierite with a low expansion coefficient was successfully prepared from FS and quartz. The composition and structural characteristics of FS were analyzed. The phase evolution, microstructure, coefficient of thermal expansion (CTE), and material properties were studied. With 34 wt% quartz and maximum cordierite crystal content of 75.1 wt%, the glass phase decreased from 78.7 to 12.7 wt%. The melted quartz generated silica-rich microdomains with high viscosity during heating. Subsequently, the nuclear dynamic conditions were improved to promote the formation of cordierite crystals. Appropriate sintering temperature and holding time can boost the crystallization rate of the glass phase. Further, the diffusion of silica-rich microdomains was beneficial for the formation of cordierite crystals. Finally, the optimal cordierite ceramic material was obtained at 1300 °C for 2 h with a flexural strength of 38.3 MPa and CTE of 3.01 × 10−6/°C. These studies provide an effective way of re-utilizing large volumes of FS, and suggest a new method for preparing ceramic materials using high-temperature silicate waste residues. [ABSTRACT FROM AUTHOR]

The present research aims to analyze the comminution behavior of ferrochrome slag using high-pressure grinding rolls. The laboratory bench scale high-pressure grinding rolls were used to study the three significant variables on the grinding efficiency of ferrochrome slag. The Central Composite Design was used to study the process variables, such as roll gap, applied load, and roller speed. The grinding efficiency was evaluated based on the product size and the energy consumption. The results showed that the increased gap between the rolls and roller speed decreases the product size with increased energy consumption. The results also found that an increase in applied load decreases the product fineness with increased energy consumption. The models were developed for the responses of P80 (size of 80% mass finer) and Ecs (specific energy consumption). Both the responses show high regression coefficients, thus ensuring adequate models with the experimental data. The minimum values of the P80 size and specific energy were determined using quadratic programming. The optimum values of the roll gap applied load and roll speed were found to be 1.43 mm, 16 kN, and 800 Rpm, respectively. The minimum values of P80 and the specific energy consumption were found to be 1264 µm and 0.56 kWh/t, respectively. [ABSTRACT FROM AUTHOR]

The circular economy initiative has driven the agriculture and agro-based industry to beneficiate from waste,thus closing the material loop towards enhancing economic and environmental performance. In this study, the aim was to recover phosphorus from anaerobic digestate of piggery wastewater (ADPW) using ferrochrome slag (FCSL) as the magnesium source to improve the environmental and economic sustainability of struvite precipitation. This was achieved by leaching 100 g L−1 of ferrochrome slag with 5 M HCl where 14.02 g L−1 of magnesium ions were extracted, and this acid-leachate of ferrochrome slag also contained 2650 mg L−1 of total iron. To simultaneously remove both high concentrations of organic matters in ADPW and iron in FCSL which are known to be detrimental to struvite precipitation, hydrogen peroxide (H2O2) at an H2O2/Fe molar ratio of 0.75 and pH 4.0 was added to the mixture of ADPW and FCSL. After the Fenton reaction, removal efficiencies of chemical oxygen demand (COD) and total iron reached 95.06% and 94.00%, respectively. Then COD and an iron-reduced mixture of ADPW and FCSL were added with a satisfying Mg:N:P molar ratio of 1.2:1:1.15 at pH 9.5 to produce struvite in 1 h. From 1 L of ADPW (2.6 g NH3–N), 0.5 L of FCSL (5.34 g Mg2+), and 6.62 g of PO43− P, were consumed to produce 45.57 g of struvite precipitate. Additionally, the economic feasibility of ferrochrome slag was assessed by estimating the chemical costs of FCSL against that of magnesium chloride which is commercially used. It was observed that using FCSL was cheaper as compared to using commercial MgCl2. Response surface methodology coupled with the central composite design was applied as a statistical tool to determine the effects of the key parameters (N:P; Mg:PO4; pH) on phosphorus recovery. Second-order polynomial equations were determined to correlate the parameters. ANOVA was applied and showed that p values for all the investigated parameters were less than 0.05 showing that they had a statistically significant effect on the phosphorus recovery. The study confirmed that it was possible to recover phosphorus as struvite from anaerobic digestate of pig manure with ferrochrome slag as a magnesium source.

In this study, high-carbon ferrochrome slag powder produced by grinding was used to replace different proportions of cement, and the effect of the amount of ferrochrome slag powder on the physical and mechanical properties of ferrochrome-slag-cement composites was analyzed. Water-cooled ferrochrome slag with a particle size of <5 mm was optimized to replace part of river sand as fine aggregate, and air-cooled ferrochrome slag with a particle size of >5 mm was used to completely replace coarse aggregate to prepare ferrochrome-slag-based concretes. The microstructure of ferrochrome-slag-cement composites was analyzed by X-ray diffraction, scanning electron microscopy, and thermogravimetry–differential scanning calorimetry analysis. The compressive strength, water absorption, and aggregate–slurry interface bonding properties of ferrochrome-slag-based concrete were studied. The results demonstrate that a ferrochrome slag powder amount of 15% leads to the highest performance of ferrochrome-slag-cement composite material, and the fluidity ratio of ferrochrome-slag-cement mortar is 103, higher than reference samples. Furthermore, the compressive strengths of ferrochrome slag concretes are 15.8% and 3.6% higher than conventional concrete, and the water absorption of ferrochrome slag low-carbon concrete is better than that of conventional concrete. The interface bonding structure between concrete aggregate and slurry was optimized. This research can provide a reference for studying the application of ferrochrome slag, both the feasibility of high-carbon ferrochrome slag powder as supplementary cementitious material and the application of ferrochrome slag as concrete aggregate, and it can help to achieve the purpose of saving energy and reducing carbon emissions. [ABSTRACT FROM AUTHOR]

The ever-increasing demand for ferrochrome alloys has resulted in a substantial accumulation of ferrochrome slag by-products in many mining areas. On the other hand, the ferrochrome slag has been identified as one waste material that is rich in magnesium (Mg) and has not been effectively exploited. Beneficiating of ferrochrome slag (FCS) waste material is envisaged as a means of achieving sustainable recovery of Mg. Previous studies have used sulphuric acid as a lixiviant for leaching FCS at moderate temperatures to recover Mg. In this study, the recovery of Mg from ferrochrome slag was investigated using hydrochloric acid (HCl) as the lixiviant at low temperatures. Previous studies have shown that various metal oxides have been proven to be more amenable to leaching using HCl. This study examined the effects of acid content, leaching temperature, and reaction time on the recovery of Mg from FCS. Kinetic and thermodynamic analysis of the leaching process were also investigated as these are critical factors for maximum extraction of the Mg. The results showed that the highest recovery of Mg of 88.2% was obtained from FCS using 5 M HCl with a solid to liquid ratio of 1:10, mixing intensity of 250 rpm, reaction time and temperature of 150 min and 70 °C, respectively. The shrinking core model (SCM) was used in kinetic analysis to find the experimental data's best fit. A linear relationship was obtained with the coefficient of determination for the chemical reaction model (Kc) of >0.9 which indicates a good fit. The activation energy obtained for the diffusion and chemical reaction models were 95.44 and 41.45 kJ/mol, respectively, demonstrating that the rate-limiting phase is the one involving the chemical reaction.

The present research aims to analyze the comminution behavior of ferrochrome slag using high-pressure grinding rolls. The laboratory bench scale high-pressure grinding rolls were used to study the three significant variables on the grinding efficiency of ferrochrome slag. The Central Composite Design was used to study the process variables, such as roll gap, applied load, and roller speed. The grinding efficiency was evaluated based on the product size and the energy consumption. The results showed that the increased gap between the rolls and roller speed decreases the product size with increased energy consumption. The results also found that an increase in applied load decreases the product fineness with increased energy consumption. The models were developed for the responses of P80 (size of 80% mass finer) and Ecs (specific energy consumption). Both the responses show high regression coefficients, thus ensuring adequate models with the experimental data. The minimum values of the P80 size and specific energy were determined using quadratic programming. The optimum values of the roll gap applied load and roll speed were found to be 1.43 mm, 16 kN, and 800 Rpm, respectively. The minimum values of P80 and the specific energy consumption were found to be 1264 µm and 0.56 kWh/t, respectively.

Ferrochrome slag (FCS) possesses promising properties that promote its use as an alternative to natural aggregates in concrete production. Still, there is a concern about the effect of high-temperature exposure on the properties of concrete containing FCS aggregate. Therefore, due to durability and structural fire safety, it is necessary to evaluate the properties of FCS concrete after being exposed to elevated temperatures. The present study investigates the effect of FCS fine aggregate on the physical and mechanical properties of concrete at room and elevated temperatures (i.e., 200−1000 °C). Microstructural properties at high temperatures were also evaluated using SEM-EDS analysis. The results showed an improvement in the mechanical properties of concrete with FCS fine aggregate compared to conventional concrete. After being exposed to high temperatures, the concrete containing FCS fine aggregate showed less reduction in strength properties and mass than conventional concrete. Such improvements in mechanical and physical properties are achieved due to the chemical composition and surface texture of the FCS aggregate. Microstructural observation and ultrasonic pulse velocity confirmed that FCS concrete suffered less damage upon exposure to high temperatures. Furthermore, the effect of high temperatures on the strength properties of FCS concrete is consistent with the recommendations of the codes (Eurocode 2 and ACI 216.1).

In this study, high-carbon ferrochrome slag powder produced by grinding was used to replace different proportions of cement, and the effect of the amount of ferrochrome slag powder on the physical and mechanical properties of ferrochrome-slag-cement composites was analyzed. Water-cooled ferrochrome slag with a particle size of 5 mm was used to completely replace coarse aggregate to prepare ferrochrome-slag-based concretes. The microstructure of ferrochrome-slag-cement composites was analyzed by X-ray diffraction, scanning electron microscopy, and thermogravimetry–differential scanning calorimetry analysis. The compressive strength, water absorption, and aggregate–slurry interface bonding properties of ferrochrome-slag-based concrete were studied. The results demonstrate that a ferrochrome slag powder amount of 15% leads to the highest performance of ferrochrome-slag-cement composite material, and the fluidity ratio of ferrochrome-slag-cement mortar is 103, higher than reference samples. Furthermore, the compressive strengths of ferrochrome slag concretes are 15.8% and 3.6% higher than conventional concrete, and the water absorption of ferrochrome slag low-carbon concrete is better than that of conventional concrete. The interface bonding structure between concrete aggregate and slurry was optimized. This research can provide a reference for studying the application of ferrochrome slag, both the feasibility of high-carbon ferrochrome slag powder as supplementary cementitious material and the application of ferrochrome slag as concrete aggregate, and it can help to achieve the purpose of saving energy and reducing carbon emissions.

Lately, energy-saving attempts in the construction and building materials industry have become more popular due to the diminishing natural resources. With this motivation, we investigated the first foam glass consisting of ferrochrome slag (FS) and waste soda-lime glass (SLG) for potential use as a heat insulation material. For this, FS and SLG waste materials were valorized as main constituents, whereas a mixture of water glass (WG) & glycerol (G) and a sufficient amount of water (W) was used as a foaming agent and a moisturizer in the batch mixture, respectively. The studied series was prepared with the composition of 20FS-70SLG-xG-(8-x)WG-2W where x: 2, 4, and 6 wt%. After that, three different process temperatures (800, 825, and 850 °C), two distinct heating rates (5 and 10 °C/min), and two discrete dwell times (15 and 30 min) paved the way for the synthesis of 36 different foam glass samples. Eventually, the fabricated 36 different samples were subjected to physical, thermal, mechanical, and microstructural evaluations. According to the findings, one can say that samples synthesized with a lower G-to-WG ratio, higher process temperature, lower heating rate, and higher dwell time have the best features. From the physical property determinations, we found out that bulk density (ρ bulk) varied between 233 and 903 kg m−3 while the estimated porosity (P) ranged from 59.4 to 89.5%. Further, thermal conductivity (k) measurements demonstrated that the fabricated foam glass series provides lower values, namely from 0.038 to 0.130 W m−1 K−1. Besides, compressive strength (CS) values were found to be changing from 0.127 to 2.225 MPa. Microstructural evaluations via scanning electron microscopy (SEM) revealed the pore formations and the relevant alterations as a result of the different parameters. All in all, the authors concluded that a heat insulation material composed of nearly fully waste substances can effectively be produced. [ABSTRACT FROM AUTHOR]

Abstract Ferrochrome (FeCr) slag was used as a precursor for the synthesis of a geopolymer. The effect of KOH concentration, liquid solid ratio (L/S), content of potassium metalisicate (KS) or potassium aluminate (KA), curing time on the unconfined compressive strength (UCS) and metal leachability of the synthesised geopolymer was investigated. A 10 M KOH and an L/S of 0.26 yielded a geopolymer with a UCS 13.0 MPa after 28 d of ambient temperature curing. A 0.125 wt KS:KOH addition yielded a geopolymer with a UCS of 14.7 MPa whilst a 1.25 wt KA:KOH addition yielded a geopolymer with a UCS of 24.5 MPa. The increase in strength was due to the formation of Calcium Silicate (Aluminate) hydrate. The aluminate activated FeCr slag geopolymer was the most competent of all geopolymers synthesised as it resulted in over 97% immobilisation of Fe, Zn, Mn, Ni and Cr. The 360-d static leachability tests for the aluminate activated geopolymer yielded a metal release rate lower than 90 mg mm− 2 of the geopolymer. The aluminate activated geopolymer also was resistant to changes in wet and dry cycles as it had a UCS reduction of 42% after 10 cycles whereas the pure FeCr slag geopolymer and the silicate activated geopolymer had a UCS reduction of 91 and 72% respectively after 10 cycles. The aluminate activated geopolymer met the minimum requirements for use as a paving brick for low traffic pavements. The study provides opportunities for sustainable use of FeCr slag with minimal environmental impact.

Abstract Stability of chromium in the ferrochrome slag dumps and leachate are affected by pH, redox potential and the presence of other metallic species in the slag. It is desirable to keep chromium in slag dumps in the trivalent [Cr(III)] state because trivalent chromium is 1000 times less toxic to living organisms than the hexavalent form [Cr(VI)]. Due to the low toxicity and low mobility of Cr(III), it is recommended to convert Cr(VI) to Cr(III) wherever possible to protect the health of living organisms. In this study, the role of Cr(VI) reducing organisms for stabilising chromium in slag dumps was evaluated in the presence of iron [oxidation states Fe(II) and Fe(III)]. The study showed that stabilisation of chromium species in the trivalent state was most favourable under aerated conditions. Up to 100 mg/L Cr(VI) was reduced in less than 24 h by cultures grown under aerobic conditions in the presence of Fe(III). A much shorter time (6 h) was required to reduce the same amount of Cr(VI) in the presence of Fe(II). When oxygen was completely excluded, it was only possible to reduce 20 mg/L in about 48 h which was much slower than the removal of 100 mg/L in less than 24 h under aerated conditions. Fe(II) contributed directly to catalytic reduction of Cr(VI) reduction whereas Fe(III) was beneficial to Cr(VI) reduction up to an initial Cr(VI) concentration of 75 mg/L. Evaluation of Cr(VI) reduction kinetics showed that Cr(VI) reduction under aerobic conditions followed the non-competitively inhibited mixed-order reaction. Cr(VI) reduction in sealed reactor vessels, under anaerobic conditions, followed a modified non-competitive inhibition reaction model. The results indicate that chromium stabilisation in ferrochrome slag dumps would require maintenance of a fully aerated dump supplemented by a culture of Cr(VI) reducing organisms. Highlights • Effect of Fe (II)and Fe(III) on bioremediation of Cr(VI). • Aerobic reduction rate was higher than anaerobic reduction rate. • In situ bioremediation of Cr(VI) can be an effective remediation strategy for the ferrochrome slag dumps and leachate. [ABSTRACT FROM AUTHOR]

During ferrochrome production, slag is discarded as a waste material in huge quantities. A relatively small percentage finds application whereas majority of the slag is held in dumps. The purpose of the study is valuable utilization of ferrochrome slag. The experimental results showed that 99% removal of chromium (Cr(VI)) was achieved in 1 h by ferrochrome slag from Sukinda chromite mines water. There is an in situ generation of ferrous sulphate by the effect of oxidizing agent and iron content of ferrochrome slag which is capable of reducing Cr(VI) to trivalent chromium. Water samples surrounding the slag dumped area were checked to find out the extent of problem caused by them. There is no adverse effect of Cr on the surrounding water samples. Toxicity characteristic leaching procedure test revealed that the slag is environmentally stable. This research concludes that used ferrochrome slag could be utilized as a waste water treatment. [ABSTRACT FROM AUTHOR]

A new class of conventional and low-cement ferrochrome slag-based castables were prepared from 40 wt.% ferrochrome slag and 45 wt.% calcined bauxite. Rest fraction varied between high alumina cement (HAC) acting as hydraulic binder and calcined alumina as pore filling additive. Standard ASTM size briquettes were prepared for crushing and bending strengths evaluation, and the samples were then subjected to firing at 800, 1100 and 1300 °C for a soaking period of 3 h. The microstructure and refractory properties of the prepared castables have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), cold crushing strength, modulus of rupture and permanent linear changes (PLCs) test. Castables show good volume stability (linear change

In the construction materials industry, expensive refractories (fire clay, silica, high- aluminous, etc.), are used as the main lining materials which despite their high fire resistance are inefficient for the use in thermal aggregates with an operation temperature up to 1300 °C. The purpose of the research was to develop heat-resistant concrete on the basis of sodium silicate binder and liquid glass with application of ferrochrome slag. Studies on the use of ferrochrome slag to obtain heat-resistant concrete are quite limited. It is common to apply self-scattered ferrochrome slag as a hardener when liquid glass is used. Carbonaceous ferrochrome slag is used when getting sodium silicate binder and as a filler together with other fire-resistant materials. Therefore, development of low-component heat-resistant concrete, which contains in the binder and filler the same raw materials with uniform-phase structure, represents a certain scientific and practical interest. On the basis of carbonaceous ferrochrome slag, sodium silicate binder and heat-resistant concrete with uniform-phase structure have been developed. Also a heat-resistant concrete mix has been developed with an application of liquid glass and without any special hardener. Curing of concrete on sodium silicate binder was carried out by drying in the range of temperatures of 100-200 ° C, curing of concrete on liquid glass was done with drying in the range of temperatures of 105±5 оС. Compression strength of concrete on sodium silicate binder after drying was 26.2 MPa, compression strength of concrete on liquid glass was 25.8 MPa.

This research work is aimed to determinate a possibility of stabilization of a low-carbon ferrochrome slag into a dry slag and further recycling it into a commercial product. Research was done with petrographic analysis of the structure of the artificial stone. The influence of a commercial product on constructional and technical properties of concrete and concrete mixture was determined according to the requirements of the standards for this product. As the result of the investigations of low-carbon ferrochrome slag the common regularities of formation of minerals of CaO-SiO2-Al2O3-MgO-Cr2O3 system in artificial stone were determined. Depending on the conditions of stabilization, the main minerals, formed during industrial stabilization of slag, and the structure of stabilized slag were studied in detail. The laboratory research was done and as the result new common influence patterns of fine powdered stabilized slag upon the properties of concrete mixes and concrete were reached.

High carbon ferrochrome slag is a byproduct of High Carbon Ferrochrome (HCFeCr) production in submerged arc furnaces. The slag is conventionally tapped from the furnaces and granulated before being dumped as waste. The major uses of the slag have been in road and civil engineering construction and in production of refractories. HCFeCr slags however, contain appreciable amounts of residual ferrochrome alloy which can be liberated and recovered profitably using cheap and environmentally friendly gravity concentration methods. In this work the milling behavior of a high-carbon ferrochrome slag is investigated. Milling experiments for a typical HCFeCr slag were conducted using a 0.303 by 0.282 m laboratory ball mill to establish liberation as a function of particle size and to determine the associated key breakage parameters like the breakage function (B ij ) and selection function (S i ). The breakage parameters were obtained using the monosize fraction method by milling the following size fractions − 13.2 + 9.5 mm, − 9.5 + 5.6 mm, − 5.6 + 4 mm, − 4 + 2.8 mm, − 2.8 + 1.18 mm and − 1.18 + 0.15 mm. The effects of powder filling and mill speed were also tested experimentally. An increase in the milling speed from 75% N crit to 85% N crit caused an increase in the selection functions of different fractions however a further increase to 90% N crit resulted in a drastic reduction in the rate of milling across all size fractions. Increasing the powder filling from 40% to 60% caused a marked increase in the selection functions for the particles in the size fraction − 5.6 + 4 mm and smaller and a decrease in the selection functions for the particles in the size fraction − 9.5 + 5.6 mm and larger. A further increase in the powder filling to 80% caused a marked fall in the selection functions for all size fractions to values lower than those obtained at 40% powder filling. The results from the size by assay test-work showed that the sizes of particles that contain the highest amount of the ferrochrome alloy and the least amount of silica are in the range − 1.18 + 0.6 mm. The milling process has to maximize the generation of particles in this specific size range in order to achieve the best alloy recoveries in the downstream concentration unit. [ABSTRACT FROM AUTHOR]

Ferrochrome slag (FCS) is a by-product of ferrochrome industries and is produced during the extraction of ferrochrome from chromite ore. The chemical composition of FCS comprises of 27–33% SiO 2 , 15–25% Al 2 O 3 , 20–35% MgO, and 10–15% iron-chromium compounds. The high chromium content of FCS and the possibility of its leaching into the environment categorize FCS as hazardous waste material. For each ton of ferrochrome production, nearly 1.2–1.5 tons of FCS is generated, which becomes a significant challenge for the ferrochrome producers while managing this hazardous waste. Therefore, several research attempts have been made to observe the leaching characteristics of chromium (VI) in FCS, its stabilization, and subsequent potential utilization. The high mechanical properties of FCS have led many researchers worldwide to utilize it as a construction material. This review work has undertaken FCS's physical, chemical, and microstructural characteristics and its following utilization as a fine and coarse aggregate in producing green and sustainable concrete. Different methods of stabilizing chromium (VI), including the physical, chemical, and biological methods, are extensively discussed in this review. This article also accommodated FCS as a precursor material in geopolymer and alkali-activated binders. However, the compressive strength achieved with FCS as a binder in geopolymer is very low, and thus more studies are needed to establish the possibility of strength enhancement. The leaching aspects of geopolymers with FCS also need to be studied extensively for their successive application. Lastly, the conclusions and discussion of this study have keenly addressed the significant challenges to the safe utilization of FCS in construction applications. Also, it deliberates on how the emerging research on FCS, such as refractory, composites, and coating material, can be new avenues for its utilization without any potential threat to the environment. [Display omitted] • An extensive literature on FCS is critically reviewed, taking over 120 articles in reference. • Generation, properties, environmental issues and moderation of FCS is discussed in detail. • An in-depth discussion of FCS utilization in civil engineering applications is provided withconstructive critiques. • Advance utilization of FCS is also reported for its high-end application for economic advantages. [ABSTRACT FROM AUTHOR]

The circular economy initiative has driven the agriculture and agro-based industry to beneficiate from waste,thus closing the material loop towards enhancing economic and environmental performance. In this study, the aim was to recover phosphorus from anaerobic digestate of piggery wastewater (ADPW) using ferrochrome slag (FCSL) as the magnesium source to improve the environmental and economic sustainability of struvite precipitation. This was achieved by leaching 100 g L -1 of ferrochrome slag with 5 M HCl where 14.02 g L -1 of magnesium ions were extracted, and this acid-leachate of ferrochrome slag also contained 2650 mg L -1 of total iron. To simultaneously remove both high concentrations of organic matters in ADPW and iron in FCSL which are known to be detrimental to struvite precipitation, hydrogen peroxide (H 2 O 2 ) at an H 2 O 2 /Fe molar ratio of 0.75 and pH 4.0 was added to the mixture of ADPW and FCSL. After the Fenton reaction, removal efficiencies of chemical oxygen demand (COD) and total iron reached 95.06% and 94.00%, respectively. Then COD and an iron-reduced mixture of ADPW and FCSL were added with a satisfying Mg:N:P molar ratio of 1.2:1:1.15 at pH 9.5 to produce struvite in 1 h. From 1 L of ADPW (2.6 g NH 3 -N), 0.5 L of FCSL (5.34 g Mg 2+ ), and 6.62 g of PO 4 P, were consumed to produce 45.57 g of struvite precipitate. Additionally, the economic feasibility of ferrochrome slag was assessed by estimating the chemical costs of FCSL against that of magnesium chloride which is commercially used. It was observed that using FCSL was cheaper as compared to using commercial MgCl 3- P, were consumed to produce 45.57 g of struvite precipitate. Additionally, the economic feasibility of ferrochrome slag was assessed by estimating the chemical costs of FCSL against that of magnesium chloride which is commercially used. It was observed that using FCSL was cheaper as compared to using commercial MgCl 2 ; pH) on phosphorus recovery. Second-order polynomial equations were determined to correlate the parameters. ANOVA was applied and showed that p values for all the investigated parameters were less than 0.05 showing that they had a statistically significant effect on the phosphorus recovery. The study confirmed that it was possible to recover phosphorus as struvite from anaerobic digestate of pig manure with ferrochrome slag as a magnesium source.4 ; pH) on phosphorus recovery. Second-order polynomial equations were determined to correlate the parameters. ANOVA was applied and showed that p values for all the investigated parameters were less than 0.05 showing that they had a statistically significant effect on the phosphorus recovery. The study confirmed that it was possible to recover phosphorus as struvite from anaerobic digestate of pig manure with ferrochrome slag as a magnesium source., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Authors.)

This paper presents the study of the performance of a new geopolymer binding material exposed to sulfate attack. Geopolymer binding material was obtained by alkaline activating FS with chemical materials (NaOH and Na 2 SiO 3 ). Geopolymer concrete samples were produced by mixing this binding material with river sand and crushed sand aggregates. Test specimens were immersed in magnesium sulfate solutions (by weight 3%, 5% and 7%) for various periods of time and the durability of geopolymer concrete was investigated. The residual compressive strength (90 and 180 days), change in weight and length of samples, pH variation of solution and visual appearance of these samples were obtained experimentally. It was concluded that compressive strength of both geopolymer and Ordinary Portland Cement (OPC) based concrete samples decreases with increasing in MgSO 4 content and exposure duration. After exposed to 7% MgSO 4 solution for 180 days, the minimum decrease in compressive strength was seen 25% in geopolymer concrete samples with crushed sand aggregates. [ABSTRACT FROM AUTHOR]

The ever-increasing demand for ferrochrome alloys has resulted in a substantial accumulation of ferrochrome slag by-products in many mining areas. On the other hand, the ferrochrome slag has been identified as one waste material that is rich in magnesium (Mg) and has not been effectively exploited. Beneficiating of ferrochrome slag (FCS) waste material is envisaged as a means of achieving sustainable recovery of Mg. Previous studies have used sulphuric acid as a lixiviant for leaching FCS at moderate temperatures to recover Mg. In this study, the recovery of Mg from ferrochrome slag was investigated using hydrochloric acid (HCl) as the lixiviant at low temperatures. Previous studies have shown that various metal oxides have been proven to be more amenable to leaching using HCl. This study examined the effects of acid content, leaching temperature, and reaction time on the recovery of Mg from FCS. Kinetic and thermodynamic analysis of the leaching process were also investigated as these are critical factors for maximum extraction of the Mg. The results showed that the highest recovery of Mg of 88.2% was obtained from FCS using 5 M HCl with a solid to liquid ratio of 1:10, mixing intensity of 250 rpm, reaction time and temperature of 150 min and 70 °C, respectively. The shrinking core model (SCM) was used in kinetic analysis to find the experimental data's best fit. A linear relationship was obtained with the coefficient of determination for the chemical reaction model (K c ) of >0.9 which indicates a good fit. The activation energy obtained for the diffusion and chemical reaction models were 95.44 and 41.45 kJ/mol, respectively, demonstrating that the rate-limiting phase is the one involving the chemical reaction., Competing Interests: The authors declare no conflict of interest., (© 2022 The Author(s).)