Solvent Extraction Process for Refining Cobalt and Nickel from a “Bulk Hydroxide Precipitate” Obtained by Bioleaching of Sulfidic Mine Tailings

Abstract

A flowsheet with different solvent extraction (SX) units was tested to purify cobalt, nickel, copper, and zinc from a so-called “bulk hydroxide precipitate” (BHP) from bioleaching of sulfidic tailings. A complex pregnant leaching solution was obtained by sulfuric acid leaching of the BHP, dissolving target (>99.5%) and secondary elements (including silicon). A solvent extraction step with the chelating extractant LIX 984 was integrated into conventional Co–Ni SX refining, separating copper selectively (>99%). Subsequently, di­(2-ethylhexyl)­phosphoric acid (D2EHPA) followed by phosphinic acid (Cyanex 272) SX enabled impurity removal and cobalt separation (77%) from nickel and magnesium, respectively. Silica gel was observed in the aqueous raffinate after the Cyanex 272 SX. Dissolved silica involvement in crud/precipitate/gel formation depended on its speciation (polymerization and surface groups) during SX (pH and saponification). Interference by silica was mitigated until cobalt recovery. However, nickel could be separated with the carboxylic Versatic Acid 10 from magnesium only after silica gel filtration, as crud/precipitate formed during SX at pH 7. Advanced ultrasound-assisted antisolvent crystallization gave pure monohydrated CoSO4 and NiSO4.

Synthesis of Quaternary-Ammonium-Lignin-Based Ionic Liquids and Comparison of Extraction Behavior of Co(II) and Ni(II) with 2-Ethylhexyl Phosphoric Acid Mono-2-Ethylhexyl Ester

“…As depicted in Figure 5, the lower the equilibrium pH, the lesser amounts of Co and Ni were separated. It has been established that organo-phosphorus acid extractant (P507) releases H + during Co and Ni extraction [33], leading to pH reduction. Therefore, saponification was necessary to maintain a relatively low equilibrium pH value.…”

“…The separation and purification of cobalt from its aqueous form pose significant challenges due to the various origins, intricate parts, and comparable physical and chemical characteristics. A wide variety of separation strategies has been developed to recover valuable metals and eliminate pollution by chemical precipitation [29,30], solvent extraction [31][32][33][34], resin exchange [35], membrane separation [36], and bio-recovery [37]. The chemical precipitation method, which was previously the earliest option for cobalt and nickel separation, is now rarely used alone in modern processes due to the similar solubility and coprecipitation behavior of Co(OH) 2 and Ni(OH) 2 .…”