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Quantitative determination of most economic valuable metals in waste is the first fundamental operation of evaluating the feasibility of recycling processes. Field-portable X-ray fluorescence spectrometers (FPXRFs) represent a more practical, efficient, and economic tool in determining the elemental composition of samples with respect to conventional analytical techniques, such as atomic absorption spectrometry (AAS) and inductively coupled plasma emission spectrometry (ICP). In this paper, quick and smart determination of gold content in printed circuit boards (PCBs) of waste mobile phones was studied. The aim of the research was to combine the practicality of FPXRFs with the reliability of quantitative spectrometry analysis and evaluate the error between the two techniques. Several samples (33) of PCBs were ground to a size below 0.5 mm, and then, the powders were analyzed by FPXRFs at different acquisition times with five replications for each sample. The same analyzed samples then underwent chemical attack to determine the quantitative gold content by AAS. The obtained results were associated with FPXRFs response with the purpose of realizing a calibration curve (100–1000 mg/kg Au). The curve was validated for accuracy and precision by other PCBs waste samples, the control samples were added as standards to obtain a more reliable calibration curve. The curve was evaluated with RPD classification, regression linear, and Bolt–Altman analysis.

Typical methods for the treatment of waste pickling solutions include precipitation by alkaline reagents, most commonly calcium hydroxide. As a result, large volumes of galvanic sludge form, containing iron, calcium, sulphates, and a relatively small quantity of zinc (&lt, 20%), making Zn recovery not profitable. In summary, state-of-the-art Zn galvanization processes entail the loss of valuable metals and the irrational and expensive handling of spent pickling solutions (SPSs). The resulting conclusion is that there is room for a significant improvement in the way SPSs are treated, with the double goal of enhancing Zn galvanization methods&rsquo, economic viability and achieving a lesser impact on the environment&rsquo, s processes. The experimental results show that it is possible to use SPS as a coagulant to treat the process wastewaters, kept separated, and added with sodium hydroxide. The results in obtaining precipitates with Zn contents higher than 40%, increasing the added advantage of making Zn recovery profitable. The results show the possibility of using SPS as a coagulant in the process of physical-chemical wastewater treatment and sodium hydroxide to obtain a precipitate with a zinc content of more than 40%.

The article reports the preliminary results obtained in a pilot plant that treats a spent tetramethylammonium hydroxide (TMAH) solution, a typical chemical compound used in the microelectronics industry and massively present in wastewaters. The plant is based on three aerobic bioreactors in series, fed by a real TMAH solution effluent from the semiconductor industry. The plant ran for 14 days in continuous operating mode with a flow rate of 5 L/h; then, the plant switched to batch mode. The microbial population was analyzed to determine if microbial population changes occurred. The results indicated that TMAH degradation only occurred during the batch operation mode. The TMAH reduction was about 80% in the first reactor and complete (100%) in the second and third bioreactors. At the same time, the microorganisms increased their mass by 338%, 58%, and 1% in the first, second, and third bioreactor, respectively. The degradation intermediates confirmed the efficiency of the process and the possible reuse of water, which closes the water loop's circularity. Furthermore, a nitrate concentration of 150–250 mg/L was found in the last two bioreactors: this implies a significant presence of ammonium-oxidizing bacteria. Community genomic analysis was conducted to detect changes in the microbial community due to changes in operating conditions that could cause reactor failure if methylotrophs were washed out or outcompeted by unspecific bacteria.

Rare earth elements (REEs), independently by the economic value, have a strategic importance and are involved, as critical materials, in the competition for their supply. An innovative process with the introduction of a preliminary physicochemical treatment was proposed. The mechanical activation of waste of fluorescent powders was performed by a vibratory disc mill at different experimental conditions to optimize the process. The mechanical forces induced to the powders cause crystal structure defects with a consequent increase of rare earths leachability. Factorial experimentations and analysis of variance were studied to determine the significant effects of the investigated factors (mechanical activation time, sulfuric acid concentration, pulp density and leaching temperature), especially for terbium dissolution. The preliminary activation allows to increase terbium dissolution of 35%. Then, according to the best conditions the subsequent operations of precipitation and calcination were performed obtaining a purity of 98.3% as rare earth oxides. Based on the experimental results, the flowsheet for rare earths recovery has been proposed and implemented by SuperPro Designer, a simulation software for process analysis and mass-energy balances. Finally, this paper reports a comparison between the present process with the mechanical pre-treatment and the alternative method based on thermal pre-treatment.

The paper reports on a possible way to recycle fluid catalytic cracking catalysts (FCCCs), widely used in oil refining operations. This research proposes a novel approach that leads to a near zero-waste process. The spent FCCC was leached by 1.5 mol/L of HNO3, HCl and H2SO4 solutions at 80°C, for 3 h with a solid to liquid ratio of 20 %wt/vol. The leaching yields for cerium and lanthanum were in the range 69-82 %. The solid residues from the leaching stage were used as base material for the synthesis of the zeolites by means of a combined thermal-hydrothermal treatment. The characterization of the zeolites demonstrated that the Na-A phase was predominant over the Na-X phase. The zeolites were tested as sorbent material for CO2 separation from CH4, in order to simulate the upgrading of biogas to biomethane. The maximum adsorption rate of CO2 was 0.778 mol CO2/kg of zeolite at 3 bar, with a resulting CH4 recovery of 62 % and purity of 97 %vol. The zeolites synthesized from spent FCCC represent a feasible solution to recover such industrial waste.

In this research, micellar enhanced ultrafiltration (MEUF) is tested as a seawater pre-treatment before entering RO. The experimental tests were performed by means of monotubular ceramic membranes of 210 kDa and 1 kDa. Boron is removed from the water flow using sodium dodecyl sulphate as a surfactant. The synthetic solutions contain 5 mg/L of boron and SDS concentrations are equal to 1.15 g/L and 2.88 g/L, under and above the critical micellar concentration, respectively. Experimental data showed that MUEF is efficient in removing boron, with best performances obtained at low pressure, with a low or null surfactant concentration for 1 kDa membrane and a high surfactant concentration for 210 kDa membrane. Moreover, experimental results have been used to perform a preliminary process analysis for a hypothetic sea-water desalination plant, with MEUF as a pretreatment for the RO section. The results showed that the MEUF guarantees a boron concentration after RO below the allowed threshold, by using a single step osmosis; moreover, in this way it was possible to reduce the energy consumption thus resulting in an appreciable reduction of carbon footprint as well as of the unit cost of water.

The separation of yttrium and calcium from acid leach liquor obtained from leaching of fluorescent lamp phosphors has been investigated by solvent extraction with D2EHPA and Cyanex 272 in kerosene. The preliminary tests suggested that D2EHPA was more efficient than Cyanex 272 for separation of yttrium. The experimental tests allowed to define the best process conditions, among those investigated, to separate and recover yttrium selectively. The best separation circuit included three-stage cross current extraction with 20%v/v D2EHPA in kerosene (O/A = 1/1, room temperature, 10 min of contact, pH 0.02) and stripping step in counter current with 1.5 M sulfuric acid (O/A = 1/1, room temperature, 30 min of contact). After stripping, yttrium was recovered as oxalate by the addition of oxalic acid. According to the experimental results, a hydrometallurgical process was developed. The final recovery from leach liquor was around 90% and the grade of the final product was 97.5% as hydrated yttrium oxalate. The main impurity was sulfur, 1.28% wt, in addition to traces of other elements such as Si (0.057% wt), Zn (0.015% wt), Eu (0.14% wt) and Fe (0.02% wt).

According to the International Energy Agency (IEA), only a tiny fraction of the full potential of energy from biomass is currently exploited in the world. Biogas is a good source of energy and heat, and a clean fuel. Converting it to biomethane creates a product that combines all the benefits of natural gas with zero greenhouse gas emissions. This is important given that the methane contained in biogas is a more potent greenhouse gas than carbon dioxide (CO2). The total amount of CO2 emission avoided due to the installation of biogas plants is around 3380 ton/year, as 1 m3 of biogas corresponds to 0.70 kg of CO2 saved. In Russia, despite the huge potential, the development of bioenergy is rather on the periphery, due to the abundance of cheap hydrocarbons and the lack of government support. Based on the data from an agro-industrial plant located in Central Russia, the authors of the article demonstrate that biogas technologies could be successfully used in Russia, provided that the Russian Government adopted Western-type measures of financial incentives.

The literature is rich of scientific works regarding the recovery of yttrium and europium from red phosphors of lamps and it is poor of papers about the extraction of terbium, cerium and lanthanum from green phosphors. The red phosphors are constituted by rare earth oxides and they are more easily dissolved in the leaching step respect to the green phosphors that are rare earth phosphates. This paper was mainly focused on the recovery of rare earths from green phosphors, with major attention on terbium extraction that is the most valuable metal. Hence, an innovative process with a thermal pretreatment was proposed. Alkaline fusion with barium hydroxide and the following leaching were studied under various experimental conditions to optimize the process parameters. Statistical design of experiments and analysis of variance were performed in order to determine the main effects and interactions between the investigated factors (barium hydroxide/powders ratio, sulfuric acid concentration, leaching temperature, pulp density and leaching time) for the dissolution of each rare earth elements. The results, for most of REE considered, especially for terbium showed that barium hydroxide/powder ratio and temperature were significant with a positive effect. Concentration of sulfuric acid and pulp density were significant with a negative effect. Time of leaching instead had a very slightly positive effect. The best extraction yields, obtained under the optimal conditions, were: 99% for yttrium and europium, 80% for terbium, 65% for lanthanum, 63% for gadolinium and 60% for cerium. Therefore, rare earth oxides were produced after oxalic acid precipitation and calcination. The grade was 82.22% of yttrium oxide, 8.38% of europium oxide, 2.43% of cerium oxide, 2.29% of gadolinium oxide, 1.77% of lanthanum oxide and 1.52% of terbium oxide.

The present paper describes the experimental tests for the recycling of fluid catalytic cracking catalysts (FCCCs). The process aims at the recovery of cerium (Ce) and lanthanum (La) as well as the reuse of the leaching solid residue that represents the actual problem in terms of global amount landfilled every year. Landfilling is still the main choice for the handling of such catalysts. This novel process proposes an alternative recycling approach that leads to the production of synthetic zeolites, that have several industrial applications. FCCC was leached by 1.5 mol/L of HNO3, HCl and H2SO4 solutions at 80 °C, for 2 h with a solid to liquid ratio of 20 %wt, and the two rare earth elements were recovered by precipitation with an overall yield in the range 70–80%. The solid residues from the leaching stage were used as the base material for the synthesis of the zeolites by means of a combined thermal-hydrothermal treatment. The characterization of the zeolites demonstrated that the Na-A phase was predominant over the Na-X phase. The zeolites were tested as sorbent material for CO2 separation from CH4, in order to simulate the upgrading of biogas to biomethane. The maximum adsorption rate of CO2 was 0.778 mol CO2/kg of zeolite at 3 bar, with a resulting CH4 recovery of 62% and 97 %vol as purity. Since the results in adsorption of CO2 were not satisfying, the same zeolites were used to remove heavy metals from a synthetic wastewater solution containing three metals. Equilibrium and kinetic models were also developed in order to describe the adsorption process. The maximum adsorption load was calculated by the Langmuir isotherm and resulted to be 24–32 mg/g for Ni, 52–60 mg/g for Zn and 122–181 mg/g for Cu. The results also showed that the kinetics of the adsorption process is almost fast, as after 1 h at least 95% of zinc and copper were removed, whereas the kinetics of nickel was slower for all the three zeolites. As a conclusion, the zeolites are more efficient in metal adsorption than CO2 capture, but other applications will be tested in the future.

Heavy metal pollution of civil and industrial wastewaters represents a major problem for the environment since metal ions are non-biodegradable, have a very high toxicity, and some of them have proved to be carcinogenic. If directly discharged in sewers, metal ions may seriously damage the subsequent biological treatments in depuration plants and render treatment sludge not reusable for agriculture. On the contrary, water and sludge reuse should be a primary criterion when planning improvements for wastewater treatment plants and their adaptation to new standards. In this paper, the membrane performance (a monotubular ceramic membrane of molecular weight cutoff: 210 kDa) is investigated in the removal of nickel and cobalt ions from synthetic liquid wastes aimed at water reuse using a micellar-enhanced ultrafiltration process. The ultrafiltration membrane is used with adding an anionic surfactant (sodium dodecyl sulfate (SDS)) in a laboratory scale experimental device. The synthetic liquid waste co...

The purpose of this chapter is to summarize the current status of the recycling technologies for the recovery of rare earths (i.e., yttrium, europium, terbium, lanthanum, and cerium) from spent fluorescent lamps, cathode ray rubes, and exhausted catalysts. The uses of these elements, especially for high-tech devices are increased in the recent years and combined with the scarcity of the primary sources and the environmental impact of the technologies to extract them from ores make the recycling waste a priority. For each type of waste this chapter contains a description of the most relevant scientific works and industrial application for the treatment of the waste at the end of their life. In the second part the recycling processes developed within HydroWEEE projects (grant number 231962; 308549) were presented. From the literature analysis, it was observed that many papers were published for spent fluorescent lamps treatment, fewer studies were found for the recycling of cathode ray tubes and spent FCC catalysts. This can be explained by considering the different intrinsic economic value, infact the fluorescent lamps contain high concentration of rare earths with high value (as yttrium, europium, and terbium), instead the other types of waste have a lower concentration of rare earths that also have less economic value.

This paper presents the upgrading of a full-scale domestic wastewater treatment plant, operating in Southern Italy, modified so as to process domestic wastewaters (WW) together with liquid wastes (LW), such as leachate and digestate in an integrated manner. The two streams - domestic wastewaters and liquid wastes - are separately pre-treated and then sent into a conventional denitrification/nitrification section. The preliminary treatments consist in grinding for WW and in grinding, flocculation, biological pre-treatment and advanced oxidation (Fenton process) for LW. Several scenarios were analysed using a process simulator (SuperPro Designer®): the concentrations of the main parameters (BOD5, COD, NH4+, NO3-, metals, SST) of the effluents were estimated as a function of BOD5/COD ratio, initial leachate volume and nitrate percentage in the recycle stream. In each case study the parameter values were compared with the regulatory limits provided for by the Italian Legislative Decree n. 152/2006 for discharge in surface water bodies. The results obtained show the intervals of variation of the main process parameters that in some cases do not permit to achieve the established limits.

The paper is focused on the application of solvent extraction for the recovery of rare earth elements from sulfuric leaching solutions obtained by the dissolution of fluorescent powders of lamps. The efficiency on rare earths extractions of three extractants, Cyanex 272, Cyanex 572 and D2EHPA in kerosene were investigated as a function of pH levels. Similar extraction for all the rare earths elements were observed, but the tests performed with D2EHPA showed that for pH values less than 1, yttrium and terbium could be extracted with yields higher than the other rare earths. The orders of the extraction were determined: yttrium ≥ terbium > gadolinium ≥ europium > cerium ≥ lanthanum. Further tests showed the optimal conditions, under the investigated ones, to extract yttrium with traces of terbium and cerium from sulfate leaching solutions. According to the experimental results, operating conditions of extractions were proposed in order to establish the guidelines for the following stripping and operation steps to recover rare earths selectively or at least in groups of them. A simulation of the proposed process was performed using a specific software in order to define the mass and energy balance of the entire recycling treatment of spent lamps. © 2017 Elsevier Ltd

The aim of this research was to investigate the methyl orange degradation using hydrodynamic cavitation. The synthetic solutions simulated a real textile effluent containing dye and metals (iron and nickel) as a consequence of the corrosion of nickel-plated metal components of the plant during the production of textile materials. In the first series of experiments, the hydrodynamic cavitation was studied in terms of operating inlet pressure and pH of solution. Subsequently, a full factorial plan was performed to determine the main effects and interactions among the investigated factors: inlet pressure (pin), temperature (T), initial dye concentration (cMO/0), and treatment time (t). The results showed that inlet pressure, temperature and concentration had a significant positive effect on dye degradation, as well as the interactions temperature/dye concentration and pressure/time. The optimum operating conditions among those investigated were: cMO/0 = 5 ppm, pH = 2, pin = 0.6 MPa and t = 1 h, independently of temperature (T). In the above conditions, the degradation yields were near to 75% and the final concentration was less than 1 ppm. On the contrary, at cMO/0 = 20 ppm, pH = 2, pin = 0.6 MPa, T = 40 °C and t = 1 h, the degradation efficiency was about 56% and the final concentration was less than 9 ppm. A comparison among the experiments carried out in the absence and in the presence of iron and nickel showed that metals acted as catalysts and the energy required for the process with metal ions was 5 times smaller than that those required by the experiments conducted without the metals in solution, at the same operating conditions.

In this paper, the separation of tetramethyl ammonium hydroxide (TMAH) from synthetic liquid wastes of electronic industry is carried out by using a micellar enhanced ultrafiltration (MEUF) process. This treatment represents the first step of an integrated process, aimed at the recovery of TMAH and surfactant and water reuse. The laboratory tests are carried out with an ultrafiltration module using initial solutions having a concentration of pollutant equal to 2 g/L and by adding sodium dodecyl sulfate as a surfactant, at a concentration in the range 4–10 mM/L, that is, under and above its critical micellar concentration (CMC). The experiments have been carried out at a fixed temperature of 25°C. The obtained results showed that very good percentage removals of TMAH are achieved (99%), especially when the surfactant was above the CMC.

In this paper, the efficiency of micellar enhanced ultrafiltration technique (MEUF) was tested for the removal of yttrium and zinc ions from synthetic industrial liquid wastes. UF membranes (monotubular ceramic membranes of 210 kDa and 1 kDa molecular weight cut-off) were used with adding an anionic surfactant, sodium dodecyl sulfate (SDS). A two - level full factorial design was performed in order to evaluate the effect of molecular weight cut-off, sodium dodecyl sulfate concentration and pressure on the permeate flux and rejection yields. It was found that the single factors presented the largest influence on the permeate flux: the membrane pore size and the pressure had positive effect, instead the SDS had negative effect. Regarding the metal rejection yields the main relevant factors were the membrane pore size with a negative effect, followed by the surfactant concentration with a positive effect. The effect of the pressure seemed to be almost negligible, for zinc removal experiments had a positive effect in the interactions with the surfactant and membrane pore size. The results showed that very good removal percentages up to 99% were achieved for both metals under the following conditions: 1 kDa membrane MWCO, in the presence of the surfactant at a concentration above CMC independently of the investigated pressure.

Hydrometallurgical processes for the treatment and recovery of metals from waste electrical and electronic equipment produce wastewaters containing heavy metals. These residual solutions cannot be discharged into the sewer without an appropriate treatment. Specific wastewater treatments integrated with the hydrometallurgical processes ensure a sustainable recycling loops of the electrical wastes to maximize the metals recovery and minimize the amount of wastes and wastewaters produced. In this research activity the efficiency of ultrafiltration combined with surfactant micelles (micellar-enhanced ultrafiltration) was tested to remove metals form leach liquors obtained after leaching of NiMH spent batteries. In the micellar-enhanced ultrafiltration, a surfactant is added into the aqueous stream containing contaminants or solute above its critical micelle concentration. When the surfactant concentration exceeding this critical value, the surfactant monomers will assemble and aggregate to form micelles having diameter larger than the pore diameter of ultrafiltration membrane. Micelles containing contaminants whose diameter is larger than membrane pore size will be rejected during ultrafiltration process, leaving only water, unsolubilized contaminants and surfactant monomers in permeate stream. The experiments are carried out in a lab-scale plant, where a tubular ceramic ultrafiltration membrane is used with adding a surfactant to concentrate heavy metals in the retentate stream, producing a permeate of purified water that can be reused inside the process, thus minimizing the fresh water consumption.

The paper is focused on the study of hydrometallurgical processes for recovery of rare earths (RE) from fluid catalytic cracking catalysts (FCCC). According to the experimental results two processes were proposed: in the first one RE were recovered as double sulfates by selective precipitation with sodium hydroxide after leaching with sulfuric acid. The second approach consisted of dissolution of powder by acids, solvent extraction by (2-ethylhexyl)phosphoric acid (D2EHPA), stripping and precipitation of RE oxalates using oxalic acid. Experiments showed that solvent extraction was found to be beneficial in terms of achieving improved final products quality with greater purity (∼98%).

The microelectronics industry produces significant amounts of wastewaters containing inorganic substances such as fluorides, phosphates, and organic pollutants such as acetic acid (CH3COOH), and tetramethylammonium hydroxide (C4H13NO, TMAH). The objective of this manuscript is the description of the depuration process of three types of wastewaters, representative of real liquid wastes coming from a multinational company of semiconductor production. The first residual liquid flow (WW1) contained TMAH, the second one (WW2) contained fluorides and phosphates, while the last (WW3) was rich in nitrates, fluorides and acetic acid. Aerobic treatment of WW1 was investigated by using a lab scale reactor inoculated with an activated sludge coming from the company municipal wastewater treatment plant. Another residual industrial effluent (photoresist) was added, together with several micronutrients, to guarantee a good carbon/nitrogen ratio and a nutrient supply for bacterial growth. The results showed that after one day of acclimation, the microorganisms started to remove TMAH and 99% of degradation was reached in seven days. For WW2 and WW3, a pollutant removal of 99% was obtained by chemical precipitation with lime. An attempt was made to implement the research progress made on the laboratory-developed process at the pilot and industrial scale. To this end, a simulation of the combined process was performed by using a specific software, SuperPro Designer. The process analysis showed that the treated liquids, containing TMAH not degraded to trace levels and other residual substances, can be sent to the biological WWTP of the company for further treatment; after that, the treated water can be reused and/or discharged to surface waters.

Tetramethylammonium hydroxide (TMAH) is widely used as a solvent in the semiconductor industry. After the photo-impression process, it is necessary to remove the photoresist (PR) layer from the surface of the circuits, for this purpose, a TMAH solution is usually used. This chemical compound is highly toxic and corrosive and cannot be discharged into the environment. This study was carried out in collaboration with LFoundry (SMIC group), in order to prove the feasibility of biodegradation under aerobic conditions, using microorganisms coming from the LFoundry&rsquo, s wastewater treatment plant (WWTP) at different operating conditions. The feed composition was modified in order to add a small but increasing amount of TMAH and PR. The aim was to verify if the increase of TMAH concentration was harmful to bacteria. The feed stream, containing TMAH and PR, was the only carbon source for the metabolism of the aerobic microorganisms. The results of this study demonstrated an effective biological degradation of TMAH and showed a total removal efficiency of more than 99.3%, with a final concentration of 7 mg/L. Moreover, the kinetic parameters of the Monod model were also calculated. The results obtained from the experimental campaign were used to design a pilot plant that will treat around 25 L/h of waste TMAH/PR solution.

In the present work, the degradation of azo-dyes in aqueous solutions by using hydrodynamic cavitation is performed. Methyl orange was chosen as colorant model pollutant. During the experimental tests, the effect of various operating parameters on the decolourization efficiency was investigated. In the first series of experiments, the hydrodynamic cavitation was optimized in terms of operating inlet pressure and cavitation number to get the maximum decolorization yields of the dye, at the constant temperature of 20 °C and with an initial methyl orange concentration equal to 5 ppm. It was observed that there was an optimum inlet pressure value (4 bar) to get the best decolourization efficiency (about 32%). For the optimal configuration, in correspondence of 4 bar, a first order kinetic equal to 0.0054 min −1 and a value of electrical energy per order EEO of 3793.81 kW h m-3 were calculated. Subsequently, the combined effect of hydrodynamic cavitation and hydrogen peroxide on dye degradation has been studied. The efficiency of the HC-H2O2 system, under optimal conditions, was more than 50% in terms of dye decolourization. Finally, a series of experiments have been performed by combining hydrodynamic cavitation with the addition of hydrogen peroxide and metal ions (iron and nickel) in solution. The dye degradation became greater than 90%; this increase was explained by supposing that an induced advanced Fenton process has been generate thus improving the performance of the entire cavitation system.

The control of fouling and scaling on heat and mass transfer surfaces is of major importance in processes as superficial water treatments, since it also improves the efficiency of the whole process from an energy saving point of view. The aim of the paper is to present the experimental results obtained in the inhibition of the fouling and scaling by calcium ions on an ultrafiltration membrane surface, by using citric acid as an additive. The last is an environmentally friendly additive&minus, a so-called &ldquo, green additive&rdquo, which may represent a reliable alternative to phosphorous and nitrogen based compounds typically used as inhibitors, since it has the characteristics of being non-toxic, non-bio accumulating, and biodegradable. The experimental plant is made of a tangential flow system on a lab scale equipped with a flat sheet ultrafiltration polymeric membrane, whose cut-off is 650 nm. In the first series of experiments, the effect of water hardness and its fouling effect due to calcium ions on membrane permeability has been measured in the range of potable waters. Then, the scaling effect of high calcium concentration in solution (supersaturated conditions) has been quantified by measuring the increase in weight of the membrane, with and without the addition of citric acid as an additive, moreover, the retarding effect of citric acid has been evaluated through the measurement of the induction times for the nucleation of calcium sulfate dihydrate (used as model scalant for fouling). Experiments have been carried out at two different supersaturation ratios (S = 2.25&ndash, 2.60), at room temperature, in the absence of any additive, and with a citric acid concentration varying in the range 0.01 to 0.50 g/L. Experimental results have shown that the addition of citric acid in solution delays the induction times for gypsum crystals nucleation, moreover, it mitigates the phenomenon of membrane fouling and reduces the pressure drops by allowing an acceptable permeate flow for a longer duration.

Wastewaters from civil and industrial use, which contain high concentration of heavy metals, pose the problem for their correct disposal. They cannot be directly discharged in sewage systems, as metal ions represent a serious problem not only for human health but also for the environment. In this paper, the removal of nickel, cobalt, chromium, and zinc ions from synthetic liquid wastes was carried out, by using a micellar-enhanced ultrafiltration (MEUF) process; an ultrafiltration (UF) membrane (a monotubular ceramic of molecular weight cutoff 210 kDa) together with sodium dodecyl sulfate (SDS) as an anionic surfactant was used, in a lab-scale experimental device. The synthetic liquid contained 10-mg/L metal ions (Cr, Zn, Co, Ni), while SDS concentration varied from values above and below critical micellar concentration (CMC). The experiments were carried out at room temperature (25 °C). Results achieved showed that SDS was able to bind metal ions, resulting in a strong increase of rejection coefficient, which reached highest values in case of SDS concentration below CMC, unexpectedly.

Terbium and rare earths recovery from fluorescent powders of exhausted lamps by acid leaching with hydrochloric acid was the objective of this study. In order to investigate the factors affecting leaching a series of experiments was performed in according to a full factorial plan with four variables and two levels (42). The factors studied were temperature, concentration of acid, pulp density and leaching time. Experimental conditions of terbium dissolution were optimized by statistical analysis. The results showed that temperature and pulp density were significant with a positive and negative effect, respectively. The empirical mathematical model deducted by experimental data demonstrated that terbium content was completely dissolved under the following conditions: 90 °C, 2 M hydrochloric acid and 5% of pulp density; while when the pulp density was 15% an extraction of 83% could be obtained at 90 °C and 5 M hydrochloric acid. Finally a flow sheet for the recovery of rare earth elements was proposed. The process was tested and simulated by commercial software for the chemical processes. The mass balance of the process was calculated: from 1 ton of initial powder it was possible to obtain around 160 kg of a concentrate of rare earths having a purity of 99%. The main rare earths elements in the final product was yttrium oxide (86.43%) following by cerium oxide (4.11%), lanthanum oxide (3.18%), europium oxide (3.08%) and terbium oxide (2.20%). The estimated total recovery of the rare earths elements was around 70% for yttrium and europium and 80% for the other rare earths.

The paper is focused on the economic analysis of two hydrometallurgical processes for recovery of yttrium and other rare earth elements (REEs) from fluorescent phosphors of spent lamps. The first process includes leaching with sulphuric acid and precipitation of a mixture of oxalates by oxalic acid, the second one includes leaching with sulphuric acid, solvent extraction with D2EHPA, stripping by acid and recovery of yttrium and traces of other rare earths (REs) by precipitation with oxalic acid. In both cases the REEs were recovered as oxides by calcination of the oxalate salts. The economic analysis was estimated considering the real capacity of the HydroWEEE mobile´s plant (420 kg batch-1). For the first flow-sheet the cost of recycling comes to 4.0 € kg-1, while the revenue from the end-product is around 5.40 € kg-1. The second process is not profitable, as well as the first one, taking into account the composition of the final oxides: the cost of recycling comes to 5.2 € kg-1, while the revenue from the end-product is around 3.56 €kg-1. The process becomes profitable if the final RE oxide mixture is sold for nearly 50 € kg-1, a value rather far from the current market prices but not so unlikely since could be achieved in the incoming years, considering the significant fluctuations of the Res´ market.

In this paper, yttrium recovery from fluorescent powder of lamps and cathode ray tubes (CRTs) is described. The process for treating these materials includes the following: (a) acid leaching, (b) purification of the leach liquors using sodium hydroxide and sodium sulfide, (c) precipitation of yttrium using oxalic acid, and (d) calcinations of oxalates for production of yttrium oxides. Experimental results have shown that process conditions necessary to purify the solutions and recover yttrium strongly depend on composition of the leach liquor, in other words, whether the powder comes from treatment of CRTs or lamp. In the optimal experimental conditions, the recoveries of yttrium oxide are about 95%, 55%, and 65% for CRT, lamps, and CRT/lamp mixture (called MIX) powders, respectively. The lower yields obtained during treatments of MIX and lamp powders are probably due to the co-precipitation of yttrium together with other metals contained in the lamps powder only. Yttrium loss can be reduced to minimum changing the experimental conditions with respect to the case of the CRT process. In any case, the purity of final products from CRT, lamps, and MIX is greater than 95%. Moreover, the possibility to treat simultaneously both CRT and lamp powders is very important and interesting from an industrial point of view since it could be possible to run a single plant treating fluorescent powder coming from two different electronic wastes.

This work is focused on the recovery of yttrium and zinc from fluorescent powder of cathode ray tube (CRT). Metals are extracted by sulphuric acid in the presence of hydrogen peroxide. Leaching tests are carried out according to a 22 full factorial plan and the highest extraction yields for yttrium and zinc equal to 100% are observed under the following conditions: 3 M of sulphuric acid, 10% v/v of H2O2 concentrated solution at 30% v/v, 10% w/w pulp density, 70 °C and 3 h of reaction. Two series of precipitation tests for zinc are carried out: a 22 full factorial design and a completely randomized factorial design. In these series the factors investigated are pH of solution during the precipitation and the amount of sodium sulphide added to precipitate zinc sulphide. The data of these tests are used to describe two empirical mathematical models for zinc and yttrium precipitation yields by regression analysis. The highest precipitation yields for zinc are obtained under the following conditions: pH equal to 2–2.5% and 10–12% v/v of Na2S concentrated solution at 10% w/v. In these conditions the coprecipitation of yttrium is of 15–20%. Finally further yttrium precipitation experiments by oxalic acid on the residual solutions, after removing of zinc, show that yttrium could be recovered and calcined to obtain the final product as yttrium oxide. The achieved results allow to propose a CRT recycling process based on leaching of fluorescent powder from cathode ray tube and recovery of yttrium oxide after removing of zinc by precipitation. The final recovery of yttrium is 75–80%.

The paper is focused on the use of solvent extraction for purification of leach liquor solutions obtained by leaching of NiMH spent batteries: dissolved nickel is separated from manganese and zinc by liquid–liquid extraction using D2EHPA. Two extractants were investigated: D2EHPA and Cyanex 272 in n-dodecane, and the preliminary tests suggested that D2EHPA is more efficient to separate Mn and Zn from the leaching solutions. Under the optimized conditions it is observed that in extraction circuit a recovery > 99% of zinc and > 95% of manganese is archived. The experimental results suggested that two cross-flow liquid–liquid extraction steps are adequate to extract 100% of Zn and about 95% of Mn while the residual Ni was about 80% of its initial content. The extracted elements are stripped using a 4 M sulfuric acid solution and the stripping yields were very high, > 99% for Ni and Zn and about 98% for Mn. Finally, a possible process flowsheet to separate Mn and Zn from leach liquor of NiMH spent batteries by solvent extraction is proposed. The process includes two stages of extraction with 20% v/v of D2EHPA in n-dodecane (O/A = 1/1, room temperature, 30 min of contact, pH ≤ 2.5) and one stage of stripping with 4 M of H2SO4 (O/A = 1/0.5, room temperature, 15 min of contact). The raffinate rich in Ni has the following composition: 32 g/L of Ni, 0.87 g/L of Mn, and the aqueous liquid from the stripping step had the following concentrations: 9.86 g/L of Zn, 18 g/L of Mn and 7.33 g/L of Ni. The first solution could be treated to recover Ni, for example by precipitation, whereas the second liquid could be recycled in electrolytic section to recover metallic zinc and manganese oxide.

This work describes a hydrometallurgical process to recover rare earth and basemetals from spent NiMH batteries. Laboratory tests were conducted by using NiMH powders obtained in an industrial scale grinding process after a preliminary sieving ( The most important metals present in the initial powder were nickel (29% w/w), manganese (13% w/w), zinc (8% w/w) and rare earths (lanthanum and cerium, (5% w/w); other elements were iron (1% w/w), potassium and cobalt (2.5% w/w). The results obtained showed that two sequential leaching steps were needed to dissolve almost completely lanthanum and cerium present in the samples. In the leaching experiments three parameters were studied and optimized according to a factorial experiment: sulfuric acid concentration, acid citric concentration and temperature. The average dissolution yields after the second leaching step were 100% for manganese, cobalt, zinc and rare earths and 99% for Ni. A total recovery of RE 99% was obtained after selective precipitation. Rare earths were recovered by selective precipitation with sodium hydroxide at pH less than 2 after leaching: in these conditions a precipitate composed of lanthanum and cerium sulphates are produced. A suitable flowsheet to recover RE from NiMH spent batteries with recoveries larger than 99% has been proposed.