Synthetic Leach Solution Research Articles

Application of Anti-Solvent Crystallization for High-Purity Potash Production from K-Feldspar Leaching Solution

Potassium-containing feldspars provide a high potential for producing potash, a product with widespread use in agriculture. The present work assesses applying the anti-solvent crystallization method for the purification and recovery of high-purity muriate of potash (KCl) from feldspar leaching solutions. Initially, screening experiments were carried out on a synthetic leaching solution with the aim of analyzing the crystallization behavior of key components. Screening experiments were performed using five anti-solvents, namely methanol, ethanol, acetone, 2-propanol, and ethylene glycol. Acetone and 2-propanol were viable options for crystallization of potassium chloride. Then, the effects of anti-solvent ratio (O/A), time, and anti-solvent addition rate on potassium-chloride crystallization were further investigated using acetone and 2-propanol. A recovery of 83% of potassium was achieved when using acetone at the O/A of 5 with the addition rate of 10 mL/min, at room temperature with a hold time of 180 min. The optimum conditions for 2-propanol were determined to be similar, except for using a 5 mL/min addition rate for 79% recovery. The final muriate of potash products had a purity of over 99.9% using either of the anti-solvent. However, differences in morphology and crystal size of products were observed. Acetone-formed potash crystals were aggregates of cubic crystals with an average size of 3 microns, while 2-propanol-formed potash crystals were 20 microns in size as cubic particles with a hollow core. Despite having almost the same performance in potassium recovery, acetone was found to be a more feasible anti-solvent for potash recovery due to simpler downstream solvent recovery.

Investigation on the Effect of Mesomixing on Crystal Quality during Antisolvent Crystallization of Nd2(SO4)3·8H2O

Rare earth elements (REEs) are essential for permanent magnets that are vital for wind turbines and electric vehicles motors (EV), and are also used in a range of high-tech devices such as smartphones, digital cameras, and electronic displays. Nickel metal hydride (NiMH) batteries have been identified as a potential source due to their short lifespans and an anticipated boom in the production of EV. The aim of this study was to investigate the effect of mesomixing on crystal quality in a non-confined impinging jet mixer (NCIJM) during antisolvent crystallization of 3.2 g/L Nd2(SO4)3 from a synthetic leach solution of NiMH battery using ethanol at an O/A ratio of 1.1. The jet streams were supplied at a Reynolds number (Re) between 7500 and 15,000. The product slurry was allowed to further crystallize in a stirred batch crystallizer at a Re of 13,000 for 45 s. An average yield of 90% was achieved. Laser diffraction and scanning electron microscopy (SEM) were used for size analysis. The initial results were inconclusive due to the secondary mixing effect in the stirred batch crystallizer. Therefore, the experiments were repeated, and samples were collected immediately after mixing in the NCIJM onto a porous grid placed on a high absorbance filter paper to abruptly halt crystallization. The samples were analysed using a transmission electron microscope (TEM), and the acquired images were processed using ImageJ to obtain crystal size distributions (CSDs). It was found that the enhanced mesomixing conditions resulted in smaller crystal sizes and narrower CSDs. This was because the nucleation rate was found to be mass-transfer-limited, such that higher mesomixing intensities promoted the nucleation rate from 6 × 1012 to 5 × 1013 m−3 s−1 and, therefore, favoured the formation of smaller crystals. In parallel, intensified mesomixing resulted in uniform distribution of the supersaturation and, hence, narrowed the CSDs.

Separation of base metals from reduction smelt-alloy of spent lithium-ion batteries by ferric sulfate leaching, cementation, solvent extraction and oxidative precipitation

We propose a hydrometallurgical process to recover Ni, Co, Cu, Mn, and Fe from ferric sulfate synthetic leaching solution whose composition was similar to the real leach liquor of spent lithium-ion batteries (LIBs). Copper(II) was completely separated by cementation with iron powder at room temperature for 20 min. Afterward, H2O2 was added to the raffinate to oxidize Fe(II) to Fe(III). Multi-stage cross-current extraction with 2.0 M D2EHPA and stripping with 60% aqua regia completely removed iron from the solution. The separation of Mn(II) over Co(II) and Ni(II) was carried out by oxidative precipitation, in which Mn(II) was oxidized to MnO2 at the molar ratio NaClO to Mn(II) of 4.0 at pH 3.0. Following this, most of Co(II) together with 11% of Ni(II) were coprecipitated from the Mn(II) free filtrate at the molar ratio of NaClO to Co(II) of 7.0. From the filtrate containing Ni(II) of pH 3.0, the Ni(II) ions were completely recovered using Na2C2O4 as a precipitant at the same molar ratio of oxalate to Ni(II). Continuous experiments at the optimum condition of each step verified that Cu(II), Fe(III), and Mn(II) were completely separated by cementation, solvent extraction, and oxidative precipitation. The proposed process for base metal recovery from spent LIBs offers several advantages, such as low energy requirements and products with high purity.

Vanadium recovery from spent iron sorbent used for the treatment of mining-influenced water

Vanadium was recovered successfully from spent iron sorbent (ferric oxyhydroxide, CFH-12) using a two-step process including alkaline leaching and precipitation with CaCl2. The spent CFH-12 was collected from a field study in which a filter system was used to remove vanadium from mining-influenced water (referred to as MIW-treated CFH-12). Fresh CFH-12 was treated with synthetic vanadium solution (SVS-treated CFH-12) to compare the recovery process with the field study. First, a full factorial design was performed to optimize the precipitation process using synthetic leaching solution. The optimal conditions were found to be two times the theoretical dosage of CaCl2, a precipitation temperature of 60°C, and a precipitation pH of 12.7. Vanadium desorption from the spent sorbents was conducted using 1 M NaOH, a contact time of 30 minutes and a CFH-12 solid-to-liquid ratio of 0.15 kg/L. The results revealed that vanadium could be efficiently precipitated from the leaching solution of MIW-treated CFH-12 and SVS-treated CFH-12. A higher dosage of CaCl2 was required to recover vanadium from MIW-treated CFH-12 due to the complexity of the leaching solution, which resulted in a lower vanadium content in the product. XRD analysis showed that the product recovered from SVS-treated CFH-12 mainly contained Ca5(VO4)3OH and a small amount of CaCO3. TEM images revealed that the calcium vanadate hydroxide particles were round in shape, about 0.2–0.4 µm in size and formed aggregates. The product recovered from MIW-treated CFH-12 contained amorphous calcium vanadate and crystalline Ca(OH)2. XPS analysis confirmed that vanadium existed as V5+ in all of the recovered products.

Synthesis of N-(2-ethylhexyl)-pyridine-4-carboxamide and its synergistic behaviors with dinonylnaphthalene sulfonic acid for the selective extraction of nickel and cobalt

The hydrometallurgical process for the recovery of nickel and cobalt requires a complex and expensive impurity removal process. Solvent extraction is widely used in industry for the separation, purification, and concentration of metals. However, current commercial extractants encounter some difficulties when cobalt and nickel are extracted from solutions containing a large amount of impurities such as manganese and calcium. There is an urgent need to develop new reagents for the selective extraction of Ni and Co. In this study, N-(2-ethylhexyl)-pyridine-4-carboxamide (NEHPCA) was synthesized, and the metal extraction capacity of its synergistic solvent extraction (SSX) system with dinonylnaphthalene sulfonic acid (DNNSA) and tributyl phosphate (TBP) modifier was examined. The experimental results show that the selectivity of the new SSX system has the order Cu > Ni > Co > Zn > Mn > Ca > Al ≈ Cr (III) ≈ Mg ≈ Fe (III), with excellent selectivity for nickel and cobalt. Using an organic phase composed of 0.7 M NEHPCA, 0.35 M DNNSA, and 0.2 M TBP under 1:1O/A operation, after three-stage theoretical extraction, more than 99% of nickel and cobalt can be recovered from a synthetic leaching solution of nickel laterite ore. Mechanistic studies showed that NEHPCA and water molecules participate in the internal coordination of metals, and DNNSA provided coordination anions to achieve charge balance, forming the Ni complex in this SSX system which existed most likely in the form of [Ni(NEHPCA)2(H2O)4](DNNS)2 in the organic phase.

Manganese recycling of spent lithium-ion batteries via solvent extraction

• Recycling of spent LiNi 0.33 Mn 0.33 Co 0.33 O 2 (NMC) active material from lithium ion batteries. • Continuous extraction of manganese from synthetic leaching solution with 100 g/L D2EHPA. • Correlations for Sauter mean diameter and holdup. • Mass transfer for cobalt, manganese and nickel in a disc and doughnut column. • Influence of feed pH value on selectivity and extraction yield. Solvent extraction of manganese was performed in a lab-scale DN50 pulsed disc and doughnut column. Optimal conditions for hydrodynamics and mass transfer were evaluated for the separation of manganese from cobalt and nickel with 100 g L -1 D2EHPA (di-(2-ethylhexyl) phosphoric acid) as a liquid ion exchanger. In performance tests with 0.01 mol L -1 MnSO 4 solution a maximum extraction yield of 94% was achieved at a phase ratio of 1.2 and a pulsation intensity of 3.2 cm s −1 . Statistical analysis showed that the column loading (12 and 24 m h −1 ) had no significant influence on the extraction performance. The feed was a synthetic leaching solution likewise from active material of spent Li-NMC (nickel-manganese-cobalt) ion batteries. It consisted of an equimolar solution of 0.01 mol L -1 cobalt, manganese and nickel sulfate. Highest extraction yields of manganese 84% resulted at a feed pH of 2.7 or higher. At a pH of 2.2 the selectivity had its maximum at 40 and 22 for Mn to Ni and Mn to Co, respectively. A feed pH of 2.7 is recommended for optimum extraction performance and selectivity.

Environmentally sound technology development for processing of rare earth elements from waste permanent magnets synthetic leach solutions: recovery and separation perspectives

Overall environmentally sound technology development for the waste permanent magnets (PMs) processing for the recovery of the rare earths. • The present research and development is concern to recover the rare earths from waste permanent magnets leach liquors. • From this study appropriate experimental condition for crowding studies were optimized. • Based on crowding effect, to enrich the as maximum as separation of rare earths each other. • Extraction isotherm was constructed for dysprosium. • Maximum extraction and predicted the A/O 1, 2 and 3 ratios requires 3, 5 and 8 extraction stages. An environmentally sound process was investigated as feasible to extract and separate rare earths from the synthetic leach liquors prepared based on waste permanent magnets composition analogs. Solvent extraction methods were used to screen different extractants to optimize and suggest the proper extraction system to recovery the different rare earth elements (REEs). Various experimental factors, equilibrium pH and impact of the extractant concentration were studied to select the optimum extraction system. Waste permanent magnets were treated in the initial stages with plating separation, sulfuric acid leaching and double salt precipitation. A second leaching process was implemented by hydrochloric acid; the leach liquor was treated by hydrometallurgy processes for the reprocessing and separation of rare earths present. Three phosphorous based commercial extractants Cyanex 272 (bis (2, 4, 4-trimethylpentyl) phosphinic acid), D2EHPA (bis (2, 4, 4-tri-methyl-pentyl) phosphinic acid) and PC 88A (2-ethyl-hexyl-phosphonic acid mono-2-ethyl-hexyl ester) were applied in the present study. Initial experiments suggested that Cyanex 272 is the best reagent for recovery and potential separation between REs, therefore the crowding studies were carried on. From this study appropriate experimental conditions for crowding were optimized to maximize the enrichment of rare earths while separating them.

Development of heterogeneous equilibrium model for lithium solvent extraction using organophosphinic acid

End-of-life lithium-ion batteries can be recycled to manufacture new batteries. The focus of this study is the application of solvent extraction technology for lithium ion recovery from synthetic leach solutions. This study demonstrates that an organic solvent containing Cyanex 272, tributyl phosphate and kerosene can be used for this purpose. Additionally, a new heterogeneous equilibrium model for extraction is proposed and validated using experimental data. Both the model, and the isotherm test results obtained indicate that pH, extractant concentration and multivalent metal concentration (Co(II)) significantly impact lithium extraction, while the impact of temperature, ionic strength, monovalent metals (Na(I)) and modifier concentration is minimal.

Optimization of vanadium(V) extraction by 2-ethyl-1-hexanol and the study of extraction reaction mechanism

The aims of the present work are to investigate the mechanism and thermodynamics of pentavalent vanadium (V(V)) extraction by 2-ethyl-1-hexanol and to optimize the extraction process. The stoichiometry of V(V) extraction reaction and the extraction equilibrium constants at different temperatures were determined using the slope analysis method applied to the experimental data. It was shown that the extracted V(V) was in the form of HVO3(ROH) in the organic phase. The standard enthalpy and the standard entropy of extraction reaction were calculated as 39.56 kJ/mol and 54.38 J/(mol.K), respectively. A statistical experimental design method, including Plackett-Burman design (PBD) followed by a central composite design (CCD), was employed to obtain the regression models for the prediction of extraction percentages and to optimize the recovery of V(V) from a synthetic leach solution containing Fe(III), U(VI), Si(IV), and Al(III). The accuracy of the predictive models was proven by the analysis of variance (ANOVA). The optimum condition for selective separation of V(V) was: initial pH of 1.9, extractant concentration of 70 %v/v, and T=59.3 °C. Under the optimum condition, the extraction percentages for V(V), Fe(III), U(VI), Si(IV), and Al(III) were 91.3%, 1.7%, 6.3%, 10.6%, 2.7%, respectively. Developed models were validated by solvent extraction experiments at optimum conditions.

Extraction behavior of germanium from synthetic leaching solution of secondary zinc oxide in tertiary amine (N235)-trioctyl phosphate (TOP) system

In continuation with our previous work, in the present study, the tertiary amine-trioctyl phosphate-sulfonated kerosene system was employed to recover Ge(IV) from the synthetic leachate of secondary zinc oxide. The effects of different complexing agents (tartaric acid, citric acid, oxalic acid, gallic acid, and salicylic acid) and impurities (Zn(II), Fe(III), Cd(II), Si(IV), and As(III)) on the extraction of Ge(IV) were investigated. Under comparable conditions, the extraction of Ge(IV) with the aforementioned complexants had the following order in terms of extraction efficiency: tartaric acid > citric acid > gallic acid > oxalic acid, or salicylic acid. The reason for the low extraction efficiency of Ge(IV) with the addition of oxalic acid was revealed by an extraction comparison using pure germanium and polymetallic solutions. Furthermore, a stoichiometry analysis of the extracted complex indicated that the extracted Ge(IV)-organic species was R3NH·Ge(OH)4(HT)·0.5TOP with the addition of tartaric acid. The concentration of Ge(IV) in the loaded organic phase was less than 1 mg/L when three-stage countercurrent stripping was adopted at an O/A ratio of 1/3 and 25 °C for 10.5 min.

Structure investigation for nickel and cobalt complexes formed during solvent extraction with the extractants Cyanex 272, Versatic 10 and their mixtures

This work reports the structure investigation of organometallic complexes formation between nickel and cobalt and the extractants Cyanex 272, Versatic 10 and their mixtures. For a better understanding of nickel and cobalt purification from solvent extraction technique, the experiments were carried out with a synthetic leach solution similar to the nickel laterite leach liquor. The coordination number of the metal complexes was evaluated by the ultraviolet–visible (UV–vis) absorption spectra of the organic phases after extraction. The results indicated that the nickel complexes exhibited an octahedral coordination geometry in all investigated organic phases. The cobalt-Versatic 10 complex showed an octahedral geometry, while for Cyanex 272 and the extractants mixture of 15% (v/v) Cyanex 272 and 5% (v/v) Versatic 10 (C15V5), the cobalt complexes presented a tetrahedral structure. Attenuated total reflectance with Fourier transform infrared spectroscopy (ATR/FTIR) was used to identify the interactions between the functional groups of the extractant and the metal ions. Thermogravimetric analysis (TGA) was used to examine the hydration of the complexes. The continuous variation method (Job’s method) was applied to determine the number of molecules involved in the metal-extractant complexes. The Ni-Versatic 10 complex was formed by three molecules of the extractant. For Ni-C15V5 complex, one molecule of Cyanex 272, one of Versatic 10 and two molecules of water formed the complex. For Co-Cyanex 272 and Co-C15V5, the complex was formed with two molecules of Cyanex 272, indicating that in this experimental condition there was no interaction of the extractant Versatic 10 in the extraction. After the stoichiometry of all the organometallic complexes formed had been defined, a structure was proposed for each metal-extractant complex.

Thermodynamic Model for the Design of a Process of Production of Copper Sulfate Pentahydrate from Copper Ores.

In Chile, one of the ways in which small-scale mining industries sustain themselves is through the sale of copper ores to the state company ENAMI, which monetizes this product depending on the copper’s mineral grade. To sell this mineral, small mining companies must transport the product to ENAMI, which means a high monetary cost, added to the fact that there are large amounts of waste minerals that cannot be sold because of their low grade. The present work aims that small miners can process these copper ores in situ to commercialize a more valuable product, such as copper salts. Considering the high solar radiation and the scarce superficial water resources found in the north side of the country, a possible process alternative is the leaching of the ores using acid seawater solutions followed by crystallization by solar evaporation. As a necessary tool for this process design, the present work has developed a model able to predict the copper sulfate pentahydrate crystallization from multicomponent solutions, preventing the co-precipitation of undesired compounds (such as iron salts, sodium chloride, and sodium sulphate among others) that contaminate the final product. The Pitzer thermodynamic model was successfully applied to predict the crystallization process of copper sulfate pentahydrate from synthetic leaching solutions. These results were validated through experimental tests.

Recovery of rhenium(VII) from synthetic leaching solutions of uranium ore using ionic liquid modified cellulose microsphere adsorbents

Although various novel adsorbents with different structures are exploited for rhenium recovery, developing cost-effective micron-sized adsorbents with high adsorption capacity, rapid uptake, and excellent selectivity is still challenging from a practical point of view. In current work, two ionic liquid functionalized cellulose microsphere (ILFC-NO3 and ILFC-Cl) were prepared via radiation technique and their performance for Re(VII) separation was investigated through batch and dynamic experiments. The ILFC-NO3 and ILFC-Cl exhibited not only high adsorption capacity (ILFC-NO3 of 581 mg/g and ILFC-Cl of 552 mg/g) for the high concentration of Re(VII) but also fast adsorption rate with equilibrium time of 1.5 h. Adsorption-desorption experiments indicated that both ILFC-NO3 and ILFC-Cl had excellent reusability and could be recycled four times with negligible capacity loss. Their adsorption mechanism could be explained as the combination of ion exchange and reduction. Furthermore, ILFC-NO3 could recover trace Re(VII) at 10 ppb from aqueous solution with the enrichment factor of 417. The ILFC-NO3 also exhibited excellent Re/U selectivity from synthetic uranium underground leaching solution in which the concentration of U was 200 times higher than Re(VII). This work provided two micron-sized adsorbents with superior adsorption capacity for Re(VII) recovery, which are promising candidate adsorbents for Re(VII) recovery in practical applications.

Chelating polymers with valuable sorption potential for development of precious metal recycling technologies

Abstract A special attention is currently focused on the recovery of Au, Ag, Pt, Pd and Rh from both primary and secondary sources. From the wide range of sorbents that have been used in this respect, the required selectivity is proved only by the chelating polymers containing donor N, O and S atoms in their functional groups. This work presents the recent published researches on this topic, pointing out the capabilities of chelating sorbents based on organic synthetic polymers for a sustainable development. The chelating sorbents are differentiated and reviewed according to their synthesis strategy and compatibility with synthetic and real matrices. First, an overview on the novel functionalized polymers and impregnated resins with good selectivity for the recovery of most valuable precious metals from synthetic leach solutions is given. Subsequently, the performances of these materials in the selective and preconcentrative recovery of Au, Ag, Pt, Pd and Rh from simulated and real leachates are discussed. The viability of an integrated approach for the determination of precious metals from simulated solutions by solid phase spectrometry is highlighted. The transposition of chelating polymers’ potential in challenging technologies for precious metal recovery-reuse-recycling needs further research on directions that are proposed.

Use of polyethylenimine functionalised magnetic nanoparticles for gold thiosulfate recovery

The use of calcium thiosulfate (CaS2O3) as an alternative lixiviant to cyanide to treat double refractory gold ores has become an industrial reality. In this study, a novel adsorbent, polyethylenimine coated iron oxide magnetic nanoparticles (PEI-MNPs), was evaluated for the adsorption of gold from thiosulfate leaching systems that contain gold, copper and calcium thiosulfate. Particles were characterised in terms of their size and morphology, zeta potential, crystalline structure, surface properties, functional groups, magnetic properties and thermal degradation properties. The effect of nanoparticle dosage, thiosulfate concentration, copper concentration, solution pH and solution temperature on gold loading in synthetic leaching solutions was examined. In addition, adsorption kinetics and adsorption isotherms were investigated. PEI-MNPs demonstrated a positive surface charge up to a pH of 11, which facilitated electrostatic attraction of anionic gold thiosulfate complex. A higher nanoparticle dosage, lower free thiosulfate concentrations and lower temperatures favoured gold adsorption, while copper concentration and solution pH did not show a considerable effect. Gold adsorption kinetics were fast, irrespective of the solution content and reached equilibrium in less than 30 min. The adsorption isotherm data could be fitted with both the Langmuir and the Freundlich isotherm models. The adsorbent was able to be reused after a selective metal elution process.

Recovery of Ge(IV) from synthetic leaching solution of secondary zinc oxide by solvent extraction using tertiary amine (N235) as extractant and trioctyl phosphate (TOP) as modifier

The N235–TOP–sulfonated kerosene system was applied for the recovery of Ge(IV) from a synthetic sulfuric acid leaching solution of secondary zinc oxide, containing Ge(IV), Zn(II), As(III), Fe(III), Si(IV), and Cd(II). The co-extraction of As(III) with Ge(IV) is a challenging problem in the extraction of Ge(IV) from aqueous solution by N235. However, TOP, as a modifier, suppressed the co-extraction of As(III) significantly. The effects of factors including N235 concentration, extraction time, tartaric acid to Ge(IV) molar ratio and temperature on the extractions of Ge(IV) and As(III) were studied. At an organic/aqueous (O/A) phase ratio of 1/1, aqueous phase pH of 1.2, extraction time of 10.5 min, tartaric acid-to-Ge(IV) molar ratio of 5.0, and temperature of 25 °C, the extraction efficiency of Ge(IV) reached 93.9%, whereas only 1.3% of As(III) was extracted by the 25%(v/v)N235–10%(v/v) TOP–sulfonated kerosene system in a single stage extraction. The Ge(IV) in the raffinate was less than 1.5 mg/L when employing a five-stage continuous countercurrent extraction at an O/A ratio of 1/10. In addition, aqueous NaOH solution of 0.5 mol/L was an appropriate reagent for the stripping of both Ge(IV) and As(III) at an O/A ratio of 1/1 and 25 °C for 10.0 min.

Solvent Extraction and Separation of Nd, Pr and Dy from Leach Liquor of Waste NdFeB Magnet Using the Nitrate Form of Mextral® 336At in the Presence of Aquo-Complexing Agent EDTA

Solvent extraction and separation of Pr, Nd and Dy from a synthetic leach solution of spent NdFeB magnet from wind turbines in the presence of aquo-complexing agent Ethylenediaminetetraacetic acid (EDTA) was studied using the nitrate form of Mextral® 336At ([336At][NO3]) as an extractant. The effect of different process parameters such as pH, extractant, nitrate, and EDTA concentrations on the extraction of Pr, Nd and Dy was studied. The extraction of these rare earths elements follows the order Pr > Nd > Dy, whereas EDTA forms stable complexes in the order Dy > Nd > Pr. The synergy of these two effects improved the selectivity among these elements as compared to when no aquo-complexing agent was used. The mechanism of extraction of rare earth elements was established by slope analysis method. The Fourier-Transform Infrared Spectroscopy (FTIR) spectra of [336At][NO3] and extracted Nd complex were recorded to understand the interaction of extractant with rare earth metal ions in the organic phase.

Recovery of Mo by liquid-liquid extraction from synthetic leaching solution of spent Inconel 713C super alloy and preparation of Mo compounds

Recovery of Mo by liquid-liquid extraction from synthetic leaching solution of spent Inconel 713C super alloy and preparation of Mo compounds

Iron, aluminium and chromium co-removal from atmospheric nickel laterite leach solutions

Atmospheric leaching (AL) of low-grade nickel laterite ores often produces leach liquor containing significant amounts of trivalent iron, aluminium and chromium ions. These impurities are normally removed by increasing the leach liquor pH to precipitate these metals before the recovery of nickel, cobalt and other metal values. This paper documents an investigation of the removal of iron, aluminium and chromium from both synthetic and real nickel laterite AL leach solutions using single- and multi-stage precipitation methods. Single-stage precipitation experiments performed using synthetic leach solutions containing Fe(III) + Ni(II) + Al(III), Fe(III) + Ni(II) + Cr(III), and Fe(III) + Ni(II) + Al(III) + Cr(III) showed that greater losses of nickel to solids occurred in the presence of aluminium and chromium. Increasing the pH value of the solution and the precipitation temperature favoured the removal of iron, aluminium and chromium, but at a cost of greater nickel losses. However, by carefully controlling pH and temperature using a multi-stage precipitation process, the iron, aluminium and chromium can be rejected effectively by precipitation with minimal nickel loss and desirable sludge properties. The optimum conditions for a multi-stage precipitation process were found to be pH 3.0 and 55 °C in the first stage and pH 3.0 and 85 °C in the second stage. Using this approach, as much as 95% iron and chromium together with more than 80% aluminium can be removed; the level of nickel loss to the solid can be reduced to below 1%. The sludge showed a fast settling rate of 5.05 m/h following the addition of a cationic flocculant. Similar satisfactory results were also obtained when performing this multi-stage precipitation procedure with real leach solutions.

Precipitation of Ru, Rh and Ir with iron ions from synthetic nickel sulphate leach solutions

The nickel sulphate leach solution produced in the first leaching stage of base metal refineries contains impurities such as iron as well as other precious metals (OPMs, i.e. ruthenium, rhodium and iridium). Precipitation of the dissolved iron in downstream unit operations leads to sludge formation. Some of the other precious metals have been reported to co-precipitate in the sludge; this could be used as a mechanism for OPM recovery. The objective of this study was to investigate the precipitation behaviour of OPMs during iron sludge formation from the nickel sulphate leach solution.Precipitation tests were performed on synthetic leach solutions to investigate the effect of solution pH, temperature, metal content, iron valence state and seeding on the iron and OPM precipitation behaviour. Typical iron precipitation via hydrolysis of ferric ions was observed. The primary mechanism of OPM precipitation also involved hydrolysis reactions. The solution pH had the most significant effect on OPM precipitation. Average ruthenium precipitation and rhodium precipitation of 98.1% and 92.2%, respectively, were achieved at pH4; the iron valence state and total metal concentration had no significant effect on the OPM precipitation. More basic conditions were required for thermodynamically stable iridium species to precipitate than for ruthenium and rhodium. Seeding did not enhance OPM scavenging from the leach solution.Tests performed on plant solution confirmed that OPM precipitation by neutralisation is possible. At high nickel concentrations, nickel sulphate crystallisation contributed to sludge formation and resulted in significant iridium co-precipitation due to entrainment.