Pregnant Leach Solution Research Articles

Selective leaching of lead from lead smelter residues using EDTA.

Ethylenediaminetetraacetic acid (EDTA) has been widely used as an effective reagent for removal of lead from soil because of its high lead extraction efficiency caused by the high thermodynamic stability of the Pb(ii)–EDTA complex. In this study, EDTA was used as a lixiviant for recovery of lead from residues (matte and slag) of secondary lead smelter plants. The residues were composed mainly of iron (34–66 wt%) and lead (7–11 wt%). Leaching parameters (EDTA concentration, pH, temperature, liquid-to-solid ratio and leaching time) were optimized. The optimum leaching efficiency was achieved when leached for 1 h at room temperature using 0.05 mol L−1 EDTA at a liquid-to-solid ratio of 5 mL g−1. At such conditions, 72 to 80% of lead and less than 1% of iron were leached from both matte and slag. The high selectivity towards lead with minimal co-dissolution of iron is a major advantage since it reduces the chemical consumption and simplifies the downstream processes. Although the stability constants of the complexes Fe(iii)–EDTA, Fe(ii)–EDTA and Pb–EDTA are all large (log KS 25.1, 14.33 and 18.04, respectively), the leaching of iron was most likely limited by its presence in insoluble phases such as iron oxides, sulfides and silicates in the residues. 100% leaching of lead was achieved by a multi-step leaching process where the leaching residues were contacted three times by a fresh EDTA solution. To recover EDTA, first iron was precipitated as iron hydroxide by raising the pH of pregnant leach solution (PLS) above 12.6 using sodium hydroxide, followed by precipitation of lead as lead sulfide by adding ammonium sulfide. The recovered EDTA was successfully reused two times for leaching without significant changes in leaching yields.

Mesophilic bioleaching performance of copper, cobalt and nickel with emphasis on complex orebodies of the Democratic Republic of Congo: a review of dynamic interactions between solids loading, microbiota activity and growth

The copper, cobalt and nickel ores are still currently mined in the world. Its complex mineralogy creates extraction challenges by means of conventional metallurgical methods. Meanwhile, dealing with mesophilic strains in leaching process requires a compromise between solid loading and microbiota activity and growth. That is why, the influence of solid loading with fine or coarse particulates, the cell disturbance during the metal–microbes interactions depending upon the influence of gangue nature as well as metallic ions concentration on bacterial tolerance and the chemical and biological pathways involved in bioleaching mechanism of complex ores are summarised in detail in this paper. The current trends in mechanism research and diverse discovered set of microbiota and bacterial population coupled with bacterial adaptation methods contribute to optimise and improve the metals leaching performance and knowledge. In addition, the different existing complex mineralogical structures elaborate a main indirect mechanism with two different transitory mechanisms, before metal is converted into metal sulphate as wealthily explained in this comprehensive review. More data for cost analysis concomitant with extraction efficiency of metals using mesophilic bioleaching process are needed. However, it does not mean that other options are excluded in order to set a bio-hydrometallurgical chain. In fact, to consider also the concentration and purification of the pregnant leaching solution via phase separation and solvent extraction will be helpful. This obeys to the idea of option trees, where possible options are then systematically gaged with respect to critical criteria.

Ammonium thiosulfate extraction of gold from printed circuit boards (PCBs) of end-of-life mobile phones and its recovery from pregnant leach solution by cementation

In this study, the ammonium thiosulfate leaching of gold (Au) from printed circuit boards (PCBs) of end-of-life mobile phones and the subsequent recovery of dissolved metals from pregnant leach solution via cementation were elucidated under various conditions. Over 99% of Au was extracted from crushed PCBs (D50 = 85 μm) under the following conditions: 1 M of Na2S2O3, 10 mM of CuSO4, 1 M of ammonia/ammonium concentration, 0.1 g/10 ml of solid-to-liquid ratio, and a 24-h of leaching time in the presence of oxygen. In contrast, the recovery of Au ions via cementation was more favorable in the absence of oxygen. Among the various cementation agents evaluated, copper (Cu) was the most selective and recovered around 95% of extracted Au from the pregnant leach solution even in the presence of various coexisting metal ions. The cementation of Au exhibited two distinct kinetic regions: (1) an initially rapid rate, and (2) a more gradual and constant rate. Finally, the use of Cu plates to recover Au ions from ammonium thiosulfate pregnant solution of crushed PCBs is proposed, which could selectively recover about 80% of dissolved Au and is easier to handle and reuse compared with Cu powder.

Electrochemical recovery of tellurium from metallurgical industrial waste

The current study outlines the electrochemical recovery of tellurium from a metallurgical plant waste fraction, namely Doré slag. In the precious metals plant, tellurium is enriched to the TROF (Tilting, Rotating Oxy Fuel) furnace slag and is therefore considered to be a lost resource—although the slag itself still contains a recoverable amount of tellurium. To recover Te, the slag is first leached in aqua regia, to produce multimetal pregnant leach solution (PLS) with 421 ppm of Te and dominating dissolved elements Na, Ba, Bi, Cu, As, B, Fe and Pb (in the range of 1.4–6.4 g dm−3), as well as trace elements at the ppb to ppm scale. The exposure of slag to chloride-rich solution enables the formation of cuprous chloride complex and consequently, a decrease in the reduction potential of elemental copper. This allows improved selectivity in electrochemical recovery of Te. The results suggest that electrowinning (EW) is a preferred Te recovery method at concentrations above 300 ppm, whereas at lower concentrations EDRR is favoured. The purity of recovered tellurium is investigated with SEM–EDS (scanning electron microscope–energy dispersion spectroscopy). Based on the study, a new, combined two-stage electrochemical recovery process of tellurium from Doré slag PLS is proposed: EW followed by EDRR.Graphic abstract

Recovery of Pb and Zn from a citrate leach liquor of a roasted EAF dust using precipitation and solvent extraction

Electric arc furnace (EAF) dust is globally one of the biggest metal-containing waste fractions, with a composition that challenges the recycling of dust back to the steel process due to the high Zn and Pb content, which also prevents it from being landfilled. The current study presents a process flowsheet with zinc and lead removal from EAF dust via citric acid leaching, lead removal by precipitation, and further solvent extraction (SX) of zinc for recovery. The process produces fractions that can be directly routed back to a steel plant (leach residue), a zinc electrowinning process (pregnant leach solution, PLS), and a lead smelter (lead sulfate, PbSO4 precipitate). Moreover, zinc separation by solvent extraction from citric acid leach solution originating from EAF was performed successfully with minimal impurity content in the final electrolyte, using di(2-ethylhexyl)phosphoric acid (D2EHPA). The total lead removal from PLS was achieved with an addition of only 0.012 M sulfate ion (from sulfuric acid) at room temperature. The optimization of zinc separation via SX was performed at a temperature range of 25–55 °C varying the D2EHPA concentration (10–25 vol-%) with different O/A ratios. With an optimized EAF SX process (pH = 5, t = 15 min, T = 25 °C, CD2EHPA = 20 vol-%, O/A = 1:1) and stripping process (t = 15 min, T = 25 °C, CH2SO4 = 1 M, O/A = 3:1), the zinc content in the electrolyte could be enriched up to 50 g/L, and the amount of impurities in the solution decreased down to a level where they have no adverse effect on the zinc electrowinning process and final zinc recovery. Moreover, the iron-rich leach residue was also shown to be chemically suitable as a raw material for the EAF process. With the proposed roasting-leaching-precipitation-SX-EW unit operation, EAF dust can be converted into three different secondary raw material streams, suitable for integration into state-of-the-art processes.

Regeneration of Sn-Pb solder from waste printed circuit boards: A hydrometallurgical approach to treating waste with waste

A green approach was introduced to regenerate Sn-Pb solder from waste printed circuit boards (PCBs). For this purpose, waste Al-based heat sinks were used as cementing agent to precipitate Sn and Pb from pregnant leach solution (PLS) obtained from the dissolution of waste PCBs in HCl. 97 % and 94.9 % of Sn and Pb were recovered, respectively, under optimum conditions at Al powder size of 300 μm, Al dosage of 1.516 g/l and reaction time of 15.41 min. Thermodynamic analysis was performed to predict the effect of temperature on the main reactions relevant to the cementation process. The structure of the Sn-Pb cement changed as function of temperature, leading to enhancement of the cementation rate via improving cathodic area. Kinetic modeling indicates that product layer diffusion is the rate limiting step for Sn and Pb cementation. However, the reaction mechanism shifted to chemical reaction control at high temperatures. The results of solder characterization indicated that the melting point of solder was 184.76 °C. The electrical resistivity and conductivity of the recovered pure alloy were measured to be 34.73 μΩ-cm and 2.88 × 106 Sm−1, respectively. The characterization revealed that the regenerated product is adequate as an alternative solder alloy.

Selective liquid-liquid extraction of molybdenum (VI) and rhenium (VII) from a synthetic pregnant leach solution: Comparison between extractants and diluents

A study on the selective solvent extraction (SX) of Molybdenum (Mo) and Rhenium (Re) from a synthetic pregnant leach solution (PLS) has been carried out using two diluents: kerosene and the ionic liquid (IL) 1-octyl-3-methylimidazolium bis(trifluoromethylsufonyl)imide ([omim][Tf2N]) and two extractants: di(ethylhexyl)phosphoric acid (D2EHPA) and the IL trioctylmethylammonium bis(2-ethylhexyl) phosphinate [TOMA][D2EHP].It can be concluded that the D2EHPA extractant in kerosene achieved selective Mo-Re extractions, times was achieved when replacing kerosene with [omim][Tf2N], but this time with low extraction percentages.This work shows how ionic liquids, as extractants or diluents, can improve the selective separations in industrial metal extractions.

Recovery of High-Purity MnO2 from the Acid Leaching Solution of Spent Li-Ion Batteries

Hydrometallurgical recycling processes for spent Li-ion batteries (LIBs) often produce pregnant leach solutions (PLS) that contain metals like Co, Ni, Mn, Li, Al, etc. Although significant research has focused on the recovery of the most valuable materials (e.g., Co, Ni, Li), the reclamation of Mn from PLS is often neglected. In this study, recovery of Mn via a multi-step process based on solvent extraction with di-2-ethylhexyl phosphoric acid, scrubbing, stripping and oxidative Mn precipitation has been undertaken. The results demonstrate that more than 99% of Mn can be successfully recovered as a high-purity MnO2 product (purity > 99.5%) with almost no loss of Co, Ni and Li. In addition, the behavior of other metal elements present in the PLS were also studied in detail. Overall, this study investigates the fundamentals of Mn recovery from the complicated PLS of LIBs waste and outlines industrial process feasibility based on known unit process steps.

Representative stress crack resistance of polyolefin geomembranes used in waste management

The decrease in stress crack resistance (SCR) of geomembranes (GMBs) due to physical ageing is examined. It is shown that the SCR of a 1.5 mm high density polyethylene (HDPE) GMB immersed in municipal solid waste (MSW) leachate, deionized (DI) water, and air experienced a decrease to an equilibrium value, denoted herein as SCRm, in a few months and then did not change for the remainder of a 116-month test. The same GMB was also immersed in basic mining pregnant leach solution (PLS) and brine and a similar decrease in SCR to SCRm was observed in the first three months. For this GMB, SCRm was about 50% of the initial SCR value (i.e., SCRm ∼ 0.5·SCRo) for all incubation fluids examined. It is then shown that this behaviour is not unique. Seven other high density polyethylene (HDPE) and one blended polyolefin (BPO) GMBs are shown to experience a decrease in SCR to 0.17·SCRo ≤ SCRm ≤ 0.56·SCRo without any evidence of oxidative degradation. The magnitude of SCRm is shown to be product specific. In contrast, the one linear low density polyethylene (LLDPE) examined exhibited no such physical ageing. The implications for designing with GMBs are discussed.

Extraction of Copper and Zinc from Waste Printed Circuit Boards

The recovery of valuable metals from waste printed circuit boards (WPCBs) is crucial in order to harness their economic resources, and prevents potential environmental contamination. However, selective extraction of Cu and Zn, and the co-extraction of other metals as impurities at ambient temperature using selected lixiviants such as HCl, H2SO4, HNO3, trifluoromethanesulfonic acid (TFMS), NaOH, and mixtures of NaCl and CuCl2 was studied. It is shown that the extraction efficiencies of all the metals increased with increases in lixiviant concentrations. High selectivity of Cu and Zn toward Fe were achieved in dilute H2SO4, HNO3, TFMS, and 0.5 M NaCl + 0.1 M CuCl2, and low dissolution of Pb (<5%) was observed in all H2SO4 lixiviants. Almost 100% Zn extraction using NaOH lixiviants without trace of other metals was achieved. Therefore, 0.5 M NaCl + 0.5 M CuCl2, 1.0 M HNO3, 0.5 M H2SO4, and 1.0 M TFMS showed high extraction selectivity toward Cu and Zn with low chemical consumption, and produced pregnant leach solution rich in Cu and Zn, as well as residue containing Fe, Ni, and other metals.

Recycling of spent NiMH batteries: Integration of battery leach solution into primary Ni production using solvent extraction

The utilization of existing metallurgical infrastructure and integration of secondary process streams into primary metals production can provide advantages over separate recycling plants. This paper focuses on the integration of a pregnant leach solution (PLS) into a nickel production plant that contains Ni, Co, Zn, Mn, Fe, Al and Cd ions, derived from a NiMH recycling stream. The solution composition highlights the challenge related to spent battery investigations, as although toxic Cd is not present in NiMH battery chemistries, it ends up into the battery waste collection and prevents direct integration of the battery waste into the primary process. The aim of the study is to remove Zn, Fe, Al, Mn and Cd ions from the PLS, so that the Ni and Co remaining in solution could be integrated into the nickel production process. A two-step solvent extraction process using Di-2-ethylheyxl phosphoric acid (D2EHPA) was developed. In the first step, Zn, Al and Fe were removed at pH 1.5, whereas in the second step Cd and Mn were removed at pH 2.3. Different process parameters (pH, O/A ratio, temperature, extractant concentration, kinetics) were optimized at each step of the solvent extraction. The purified and fully integrable PLS was found to contain Ni ~28 g/L and Co ~3.7 g/L.

Application of diffusion dialysis for reduction of acidity of real pregnant leach solutions containing Ni and Co ions

ABSTRACT Diffusion dialysis (DD) was proposed as a pretreatment step to reduce the acidity of real sulfate/chloride pregnant leach solutions containing cobalt(II) and nickel(II). Optimum DD conditions that enable reduction of acidity in the feed while maintaining a high rejection level of metal ions present in PLS were proposed, e.g. for 0.06 dm3/min flow of both aqueous phases H+ concentration in the dialysate reached 3.8 and 2.99 M for PLS1 and PLS2, respectively. Acid diffusion coefficients varied from 0.32 ∙10 −6 to 3.15∙10−6 m/s and decreased with increasing phase flow rates. Moreover, dialysate neutralization was beneficial for the H+ reduction in the feed.

Recovery of copper from a mixture of printed circuit boards (PCBs) and sulphidic tailings using bioleaching and solvent extraction processes

The extraction of copper from a mixture of a Cu-Ni-Co bearing sulphidic tailing and printed circuit boards was investigated by bioleaching process followed by solvent extraction of the pregnant leach solutions. Bioleaching was conducted in both batch and continuous modes in 2- and 50-L stirred tank bioreactors using a mixed culture of iron- and sulphur-oxidizing microorganisms. The results of bioleaching in three 50-L reactors showed that 92% copper, 67% zinc and 45% aluminum were extracted in a batch mode. The process was then performed in the continuous mode in which 96.8% of copper was leached with 10 days’ residence time. Afterward, the bioleach solutions containing 2.85 g/l Cu was purified by solvent extraction with LIX 984 N extractant diluted in kerosene. The effect of some critical parameters namely extraction time, pH, stirring rate, aqueous/organic phase ratio and extractant concentration on the extraction efficiency of copper was investigated. Results showed that copper can be efficiently extracted from the bioleach solution in two stages (96% extraction). The co-extraction of zinc and nickel was increased at the higher level of pH (2.5). A new flowsheet was proposed to treat both electronic wastes and sulphidic tailings.

Laboratory Scale Investigations on Heap (Bio)leaching of Municipal Solid Waste Incineration Bottom Ash

Municipal solid waste incineration bottom ash (MSWI BA) is the main output of the municipal solid waste incineration process, both in mass and volume. It contains some heavy metals that possess market value, but may also limit the utilization of the material. This study illustrates a robust and simple heap leaching method for recovering zinc and copper from MSWI BA. Moreover, the effect of autotrophic and acidophilic bioleaching microorganisms in the system was studied. Leaching yields for zinc and copper varied between 18–53% and 6–44%, respectively. For intensified copper dissolution, aeration and possibly iron oxidizing bacteria caused clear benefits. The MSWI BA was challenging to treat. The main components, iron and aluminum, dissolved easily and unwantedly, decreasing the quality of pregnant leach solution. Moreover, the physical nature and the extreme heterogeneity of the material caused operative requirements for the heap leaching. Nevertheless, with optimized parameters, heap leaching may offer a proper solution for MSWI BA treatment.

Environmentally friendly hydrometallurgical recovery of tin and lead from waste printed circuit boards: Thermodynamic and kinetics studies

The aim of this research was to develop an environmentally friendly flowsheet to recover Sn and Pb, which are two well-known hazardous elements, from waste printed circuit boards (PCBs), resulting in solving an environmental issue besides reproducing high-value metals. In the leaching process, the highest Sn and Pb recoveries of 88% and 99% were achieved by using 2 M hydrochloric acid (HCl) at an agitation rate of 500 RPM at 75 °C. Thermodynamic evaluations were employed successfully to confirm the leaching results. The kinetics studies indicated that the reaction mechanism shifted from a mixed control model (surface reaction control and diffusion through product layer) to the diffusion control, by increasing the agitation rate. The temperature and acid concentration controlled the dissolution by the diffusion mechanism. Production of an ash layer on the particle surface suppressed Sn and Pb dissolution as a result of enhancing both the temperature and acid concentration. The results of the kinetics modeling have been validated by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) studies. The activation energies for Sn and Pb were found to be 39.49 and 50.60 kJ/mol, respectively. The Fourier-transform infrared spectroscopy (FTIR) indicated the presence of alkyne and alkyl halides, as well as carboxylic and aromatic components, in the pregnant leach solution. The metallic SnPb product was obtained by using Al-based heat sink scrap separated from the same PCBs via the cementation method. The SEM and X-ray mapping studies were carried out to characterize this product. The selectivity of the cementation method for Sn and Pb was confirmed by the above-mentioned methods.

High-Pressure Oxidative Leaching and Iodide Leaching Followed by Selective Precipitation for Recovery of Base and Precious Metals from Waste Printed Circuit Boards Ash

: This paper deals with the recovery of gold from waste printed circuit boards (WPCBs) ash by high-pressure oxidative leaching (HPOL) pre-treatment and iodide leaching followed by reduction precipitation. Base metals present in WPCB ash were removed via HPOL using a diluted sulfuric acid solution at elevated temperatures. Effects of potassium iodide concentration, hydrogen peroxide concentration, sulfuric acid concentration, leaching temperature, and leaching time on gold extraction from pure gold chips with KI–H2O2–H2SO4 were investigated. The applicability of the optimized iodide leaching process for the extraction of gold from the leach residue obtained after HPOL were examined at different pulp densities ranging from 50 g/t to 200 g/t. Results show that the removal efficiency was 99% for Cu, 95.7% for Zn, 91% for Ni, 87.3% for Al, 82% for Co, and 70% for Fe under defined conditions. Under the optimal conditions, the percentage of gold extraction from the gold chips and the residue of WPCBs was 99% and 95%, respectively. About 99% of the gold was selectively precipitated from the pregnant leach solution by sequential precipitation with sodium hydroxide and L-ascorbic acid. Finally, more than 93% of gold recovery was achieved from WPCB ash by overall combined processes.

Accelerating leaching of copper ore with surfactant and the analysis of reaction kinetics

To solve the problem of low permeability and lower extraction rates of high-mud ores, a surfactant was added as a penetrant to the pregnant leaching solution during column leaching tests. On the basis of the theories of physical chemistry and seepage flow mechanics, the mechanism by which seepage is enhanced under the effects of the surfactant was analyzed. The results show that the action modes of the surfactant were divided into four aspects: changing the wettability of the ore, reducing the viscosity of the leaching solution, adsorbing onto the surface of ore, and enhancing the permeability effect. The findings of column leaching tests demonstrated that permeability was substantially improved by the surfactant. In the later period of leaching, the permeability coefficient was two times higher than that of the control group. Meanwhile, the ore extraction rate increased by approximately 10%. During the leaching process, the surface tension of the solution did not substantially change, and that of the solution with surfactant increased slightly. The kinetics analysis of ore column leaching illustrated that the leaching processes were controlled by both internal diffusion (principal factor) and chemical reaction.

Column Bioleaching of Fluoride-Containing Secondary Copper Sulfide Ores: Experiments With Sulfobacillus thermosulfidooxidans.

Bioleaching is a mature technology, which is widely employed commercially in the leaching of primary sources of metals (ores, concentrates, and mine residues). The current work discussed the effects of aluminum sulfate additions to the growth medium, PLS recirculation and bleeding on the column bioleaching of secondary copper sulfide ores with a significant content of fluoride-containing minerals. Fluoride is toxic to bacteria at the pH of bioleaching but its toxicity may be overcome in the presence of soluble aluminum and ferric iron. Therefore, experiments were carried out in 10 × 100 cm height aerated columns, loaded with 10 kg of crushed and agglomerated copper ore and inoculated with Sulfobacillus thermosulfidooxidans. Initially, fluoride concentrations of up to 2.5 g/L in the pregnant leach solution were observed due to the fast dissolution of fluoride-bearing minerals. Aluminum was added to the leaching solution to reduce the Al/F ratio so that the concentration of HF (the main toxic species) was decreased, but while the total fluoride concentration was higher than that of aluminum, the bacterial population as low. Therefore, the current work emphasizes that it is possible to set up conditions to enable bioleaching even at high fluoride concentrations. Following this approach, copper extractions above 90% were achieved for a H2SO4 consumption ranging from 128.8 to 206.1 Kg/ton.

On the determination of manganese in the presence of iron in pregnant leach solution using derivative spectrophotometry

Mn determination in samples with high Fe content using derivative spectrophotometric method was proposed in this paper, which formaldoxime was used as chromogenic reagent. The derivative method is useful to manipulate spectra data in order to eliminate the noise spectra i.e. Fe and isolate the spectra of elements of interest (Mn). Formaldoxime was chosen since the reagent reacted both to Mn and Fe at the same pH condition. In this paper, the accuracy in Mn determination in the presence of Fe using proposed method would be assessed and discussed. Mn and Fe could be simultaneously determined Mn using zero crossing point of first derivative Fe-formaldoximate spectra at 530 nm for Mn determination, while Fe could be predicted using zero crossing point of second derivative Mn-formaldoximate spectra at 469 nm. Maximum concentration which obeyed the linearity of calibration curve is 2 and 20 mg/L for Mn and Fe, respectively. The error in Mn and Fe prediction depends on ratio of both elements.

Column leaching of low-grade saprolitic laterites and valorization of leaching residues

Socio-economic data on nickel and cobalt show their importance throughout the entire metal value chain, from mining to end use, disposal and recycling. Thus, the extraction of both metals from primary and secondary raw materials as well as from wastes is currently considered strategically important for the industry and the society. In this paper heap leaching of Greek low-grade saprolitic laterites, with Ni content 0.97%, was investigated. The main parameters studied involved the strength of the H2SO4 solution used (49 and 147gL−1) and the effect of adding sodium sulfite (Na2SO3) in the leaching medium. The pregnant leach solution (PLS) was recycled several times during leaching in order to minimize acid consumption. The experimental results showed that within a period of 25days, and under the optimum conditions (147gL−1 H2SO4 and 20gL−1 Na2SO3), i) Ni and Co extractions were 72.5% and 47.4%, respectively and ii) Fe and Al co-extractions were 8.7% and 31.3%, respectively. Furthermore, valorization of the leaching residues through alkali activation using NaOH and Na2SiO3 and the addition of metakaolin (MK) for the production of inorganic polymers (IPs) was explored. X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, Differential scanning calorimetry (DSC/TG) and Scanning electron microscopy (SEM-EDS) were used to characterize the ore, its leaching residues and the IPs. The IPs produced demonstrated high compressive strength, almost 40MPa and are suitable for a wide range of applications in the construction sector.