Removal of calcium and magnesium from lithium brine concentrate via continuous countercurrent solvent extraction. Hydrometallurgy 162, 9-15.

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Arsenic-contaminated sulfuric acid solutions are produced in large quantities as by-product during pyrometallurgical processing of sulfide minerals. Options for re-using such acid solutions are increased if the arsenic is removed and recovered as a product. The performances of tributyl phosphate and a mixture of 6 wt-% 1,2-octanediol in 2-ethylhexanol were studied in liquid-liquid extraction of arsenic from an industrial solution containing 10.4 M H2SO4. It was found that, due to the complex phase equilibria, a process design based on conventional batch equilibrium data did not describe the countercurrent processes accurately. A countercurrent flowsheet utilizing undiluted tributyl phosphate was investigated by pseudo-countercurrent extractions. 83.7 % extraction of arsenic and 31.4 % coextraction of H2SO4 was obtained in three-stage countercurrent extraction operated at a solvent-to-feed ratio of 0.79. Two-stage countercurrent scrubbing with pure water at O/A = 4.03 back-extracted 83.6 % of H2SO4 and 24.9 % of arsenic. 100 % and 89.7 % back-extraction was achieved in four-stage stripping at O/A = 2.01 for H2SO4 and arsenic, respectively. The effects of varying the flowsheet and operating parameters on separation efficiency are discussed.

With decreasing ore grades, the tailings of mining operations are becoming of increasing interest as metal-containing secondary raw materials. The objective of the current work was to investigate chloride leaching of gold, copper, cobalt, nickel, and zinc present in the flotation tailings. In the current study, the effect of cupric ion as an oxidant (0-50 g/L) and NaCl (150-250 g/L) on metals extraction was investigated. The other parameters, such as pH (1.8), temperature (95°C), solid/liquid ratio (25%), oxygen feed rate (1200 mL/min), leaching time (24 h), and stirring rate (950 rpm), were kept constant. Gold dissolution rate was shown to increase with increase in cupric ion concentrations up to 50 g/L. Also, increase in NaCl concentration up to 250 g/L increased gold extraction. Majority of the copper present in the flotation tailings could be dissolved with all the all solutions investigated. The other base metals, cobalt, nickel, and zinc extractions were also shown to increase with increase in the cupric ion and sodium chloride concentration. However, even in the absence of cupric ion addition (t = 72 h, 250 g/L NaCl), the final extraction of Cu, Ni, Zn, Co, and Fe increased up to 98, 93, 83, 76, and 80%, respectively. This shows the power of inherently originating oxidants present in the tailings. Furthermore, the solid analysis of the leach residue indicated that leaching the flotation tailings in pure NaCl may result in partial gold dissolution. The results demonstrate that significant amount of metals present in the tailings could be extracted even with only NaCl as added chemical in the presence of oxygen feed, oxidizing agents originating directly from the raw material. This can provide an advantageous cyanide-free method for extraction of metals from very low-grade tailings with low chemical consumption.

Ion exchange has not been extensively studied nor industrially used for recovering small amounts of silver from concentrated base metal-chloride solutions. A novel multistep process utilizing a weak anion exchanger with polyamine functionality is proposed and its performance investigated experimentally. Suitability of a silica based polyamine functional resin WP-1 to the task was demonstrated by comparing Ag uptake and selectivity of several ion exchange resins and adsorbents using batch equilibrium experiments. HCl was found to be the best choice for washing impurities, especially Cu, from the bed after the loading step. Tetrasodium salt of EDTA was found suitable especially for selective desorption of lead from the loaded bed, but also other impurities were scrubbed if still present after the wash. Both thiosulfate and thiourea were shown to be effective for elution of Ag from the WP-1 bed, but thiourea is preferred because of the slight affinity of thiosulfate towards the resin. Stability of the performance of the process was shown in several consecutive adsorption-elution cycles containing all the needed washing and scrubbing steps. With the developed process, 72% pure silver product was obtained. As the washing step can be designed such that no silver is lost, the recovery yield for Ag depends only on the length of the loading step, and even 100% recovery can thus be achieved for the whole process.

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