Carbon mineralization with concurrent critical metal recovery from olivine.

Carbon dioxide utilization for enhanced metal recovery (EMR) during mineralization has been recently developed as part of CCUS (carbon capture, utilization, and storage). This paper describes fundamental studies on integrating CO2 mineralization and concurrent selective metal extraction from natural olivine. Nearly 90% of nickel and cobalt extraction and mineral carbonation efficiency are achieved in a highly selective, single-step process. Direct aqueous mineral carbonation releases Ni2+ and Co2+ into aqueous solution for subsequent recovery, while Mg2+ and Fe2+ simultaneously convert to stable mineral carbonates for permanent CO2 storage. This integrated process can be completed in neutral aqueous solution. Introduction of a metal-complexing ligand during mineral carbonation aids the highly selective extraction of Ni and Co over Fe and Mg. The ligand must have higher stability for Ni-/Co- complex ions compared with the Fe(II)-/Mg- complex ions and divalent metal carbonates. This single-step process with a suitable metal-complexing ligand is robust and utilizes carbonation processes under various kinetic regimes. This fundamental study provides a framework for further development and successful application of direct aqueous mineral carbonation with concurrent EMR. The enhanced metal extraction and CO2 mineralization process may have implications for the clean energy transition, CO2 storage and utilization, and development of new critical metal resources.

Recovery of vanadium from calcification roasted-acid leaching tailing by enhanced acid leaching.

Vanadium contained tailing generated from the typical calcium roasting-acid leaching process is contaminant and waste of resource. Atmospheric and pressurized leaching were conducted and compared to recover the vanadium from the vanadium tailing and improve the tailing's environmental quality. Orthogonal experiments were designed and applied for the atmospheric leaching study. It is shown that the extraction efficiency of V changed from 29.6% to 43.5% while the extraction efficiency of Fe, Cr, Ti, Mg remained stable under 4% with variable atmospheric leaching conditions. In the pressurized leaching experiments, the effects of leaching temperature, H2SO4 concentration, liquid to solid ratio and leaching time on the extraction of V, Fe, and Ti were investigated. Under the optimum conditions (the temperature of 413.15 K, H2SO4 concentration of 300 g/L, liquid to solid ratio of 8:1 mL/g and the reaction time of 100 min), the extraction efficiencies of V, Fe, and Ti reached 91.7%, 60.1% and 46.5% respectively, a leach residue contains only 0.13% of stable vanadium was obtained.

Feasibility study on the use of thiosulfate to remediate mercury-contaminated soil.

The feasibility of using sodium thiosulfate to remediate the mercury-contaminated soil around a local chemical plant in northeastern China has been investigated. Effects of solid-to-reagent ratio and temperature on mercury extraction from soil samples with thiosulfate solutions were examined. BCR (European Community Bureau of Reference) analysis indicated that more than 90% of weak acid soluble and reducible mercury in the soil sample could be extracted by thiosulfate solution. Mercury extraction kinetics can be described by the two-step first-order reaction model in which the readily extractable fraction and the less extractable fraction of mercury were associated with their own rate constants. Mercury extraction with thiosulfate solutions could be slightly promoted when the contaminated soil was pre-oxidized with hydrogen peroxide. The results suggest that thiosulfate is a potentially effective complexing lixiviant in mercury-contaminated soil remediation.

The leaching kinetics of cadmium from hazardous Cu-Cd zinc plant residues.

A large amount of Cu-Cd zinc plant residues (CZPR) are produced from the hydrometallurgical zinc plant operations. Since these residues contain substantial amount of heavy metals including Cd, Zn and Cu, therefore, they are considered as hazardous wastes. In order to realize decontamination treatment and efficient extraction of the valuable metals from the CZPR, a comprehensive recovery process using sulfuric acid as the leaching reagent and air as the oxidizing reagent has been proposed. The effect of temperature, sulfuric acid concentration, particle size, solid/liquid ratio and stirring speed on the cadmium extraction efficiency was investigated. The leaching kinetics of cadmium was also studied. It was concluded that the cadmium leaching process was controlled by the solid film diffusion process. Moreover, the order of the reaction rate constant versus H2SO4 concentration, particle size, solid/liquid ratio and stirring speed was calculated. The XRD and SEM-EDS analysis results showed that the main phases of the secondary sulfuric acid leaching residues were lead sulfate and calcium sulfate.

The effect of coordinated water on the connectivity of uranium(IV) sulfate x-hydrate: [U(SO4)2(H2O)5]·H2O and [U(SO4)2(H2O)6]·2H2O, and a comparison with other known structures.

Two new solid-state uranium(IV) sulfate x-hydrate complexes (where x is the total number of coordinated plus solvent waters), namely catena-poly[[pentaaquauranium(IV)]-di-µ-sulfato-κ(4)O:O'] monohydrate], {[U(SO4)2(H2O)5]·H2O}n, and hexaaquabis(sulfato-κ(2)O,O')uranium(IV) dihydrate, [U(SO4)2(H2O)6]·2H2O, have been synthesized, structurally characterized by single-crystal X-ray diffraction and analyzed by vibrational (IR and Raman) spectroscopy. By comparing these structures with those of four other known uranium(IV) sulfate x-hydrates, the effect of additional coordinated water molecules on their structures has been elucidated. As the number of coordinated water molecules increases, the sulfate bonds are displaced, thus changing the binding mode of the sulfate ligands to the uranium centre. As a result, uranium(IV) sulfate x-hydrate changes from being fully crosslinked in three dimensions in the anhydrous compound, through sheet and chain linking in the tetra- and hexahydrates, to fully unlinked molecules in the octa- and nonahydrates. It can be concluded that coordinated waters play an important role in determining the structure and connectivity of U(IV) sulfate complexes.

Studies on solvent extraction of copper and cyanide from waste cyanide solution.

The recovery of copper and cyanide from waste cyanide solution with the guanidine extractant (LIX 7950) and the modified amine extractant (LIX 7820) has been investigated. Copper can be effectively extracted from alkaline cyanide solutions by both extractants. The free cyanide remains in the aqueous phase due to the preferential extraction of Cu(CN)(3)(2-) over Cu(CN)(4)(3-) and CN(-) by the extractants. The selectivity of the metals with the extractants under different cyanide levels has been examined. High cyanide levels tend to depress extraction of copper and silver cyanides, but exhibit insignificant effect on extraction of gold, zinc, nickel and iron cyanides. A possible solution to the separation of copper cyanides and free cyanide in cyanide effluents has been suggested, by which copper can be concentrated into a small volume of solution and the barren cyanide solution recycled to the cyanidation process.