Tianzu Yang

Ligand selection for complex-leaching valuable metals in hydrometallurgy

Abstract A two-stage ligand selection method composed of a primary selection and a critical selection, for complex-leaching valuable metals was presented. At the primary selection stage, three conditions were discussed under a supposed ideal state by mathematical derivation. Generally, ligands selected under condition I, were easier for complex-leaching valuable metals than that under condition II, however, under condition III, ligands selected were hard to complex-leaching the valuable metals. Ligands that were out of these three conditions could be disposed directly. In critical selection, ligands selected in primary selection can be finalized. Case applications were provided for verifying the method. The application indicated that iminodiacetate (Ida 2− ) can be used as a complex agent for complex-leaching smithsonite (ZnCO 3 ); the leaching condition should be controlled with pH 8–11; the relative error of the minimum consumption of Ida 2− between the predicted and the calculated results is 5.3%. The results indicate that the theoretical derivations in the ideal state are reliable, and the method for ligand selection is practical and operable.

Lead electrodeposition from alkaline solutions containing xylitol

Abstract The electrodeposition of lead in alkaline solutions containing xylitol (1, 2, 3, 4, 5-pentahydroxypentane) was studied. The lead electrodeposition and the chemical stability of xylitol in alkaline solutions were investigated by cyclic voltammetry. Apparent activation energy, apparent transfer coefficient and exchange current density were obtained by linear sweep voltammetry. Initial stages of lead electrocrystallization were determined by chronoamperometry. Voltammograms of a AISI 316 stainless steel electrode in xylitol solution exhibit no current in the potential range of −1.3 V to 0.75 V (vs Hg/HgO), implying that xylitol is stable to oxidation and reduction. The apparent activation energy, apparent transfer coefficient and exchange current density were calculated to be 35.15 kJ/mol, 1.56 and 9.65×10 −5 A/m 2 . Analysis of the chronoamperometric responses implies three-dimensional growth of nuclei, with the type of nucleation depending on overpotential.

Preparation of flake AgSnO2 composite powders by hydrothermal method

Abstract Silver-tin oxide composite powders and silver powders were synthesized by hydrothermal method using NH 3 to complex Ag + , SO 2− 3 to reduce Ag(NH 3 ) + 2 and Na 2 SnO 3 as the source of tin. The powders were characterized by XRD, SEM and EDX. The results show that there are macroscopic and microscopic differences between two kinds of powders. Spherical silver powders are 3 μm in diameter, and silver-tin oxide composite powders are mainly flake of about 0.3 μm in thickness. Silver crystal in silver-tin oxide composite powders is preferentially oriented in the (111) crystallographic direction and its oriented index is 2.581. Crystal lattice parameter of silver crystal of silver tin-oxide composite powders is 0.409 34 nm, larger than 0.408 68 nm of silver powders. The XPS analysis shows that silver in silver-tin oxide composite powders is metallic silver and tin oxide in silver tin-oxide composite powders has the red shift for Sn 4+ (3d 5/2 ) and O 2− (1s).

Thermodynamic analysis of separating lead and antimony in chloride system

In chloride system, thermodynamic analysis is a useful guide to separate lead and antimony as well as to understand the separation mechanism. An efficient and feasible way for separating lead and antimony was discussed. The relationships of [Pb(superscript 2+)][Cl(superscript -)]^2-lg[Cl](subscript T) and E-lg[Cl](subscript T) in Pb-Sb-Cl-H2O system were studied, and the solubilities of lead chloride at different antimony concentrations were calculated based on principle of simultaneous equilibrium. The results show that insoluble salt PbCl2 will only exist stably in a certain concentration range of chlorine ion. This concentration range of chlorine ion expands a little with increasing the concentration of antimony in the system while narrows as the system acidity increases. The solubility of Pb(superscript 2+) in solution decreases with increasing the concentration of antimony in the system, whereas increases with increasing the concentration of total chlorine. The concentration range of total chlorine causing lead solubility less than 0.005 mol/L increases monotonically.

Properties of nanocrystalline copper prepared by vacuum-warm-compaction method

Abstract Nanocrystalline Cu with average grain size of 22.8–25.3 nm was prepared by vacuum-warm-compaction method. Scanning electronic microscope, HMV-2 type microhardness tester, X-ray diffractometer, and 6157 type electrometer were used to determine the microstructure, microhardness and electrical resistivity of as-prepared nanocrystalline Cu, respectively. The results show that the microhardness of nanocrystalline Cu increases with larger pressure, longer duration of pressure or higher temperature. The highest microhardness of nanocrystalline Cu is 3.8 GPa, which is 7 times higher than that of coarse-grained copper. The electrical resistivity of as-prepared specimens is (1.2–1.4)×10 −7 Ω·m at temperature 233–293 K, which is 5–6 times higher than that of the coarse-grained copper.

Leaching of low grade zinc oxide ores in Ida2--H2O system

Abstract Ida 2- -H 2 O system (iminodiacetate aqueous solution) was used to leach a low grade zinc oxide ore for Zn extraction. The effects of leaching time, liquid-solid ratio (L/S), total concentration of Ida 2- ([Ida 2- ] t ), leaching temperature and pH on Zn leaching recovery and the dissolution of impurities such as Ca, Mg, Cu, Ni, Fe, Pb and Cd were investigated. Results show that Ca, Mg and Fe in ores were hardly dissolved in alkalescent iminodiacetate aqueous solution, while valuable metals such as Cu, Ni, Pb and Cd were partly dissolved into leaching liquor with Zn. The recovery of Zn reaches 76.6% when the ores were leached for 4 h at 70 °C by 0.9 mol/L iminodiacetate aqueous solution with pH of 8 and L/S of 5:1.

Synthesis and properties of nanocrystalline nonferrous metals prepared by flow-levitation-molding method

Abstract Nanocrystalline nonferrous metals (Cu, Al, and Ag) were synthesized by flow-levitation-molding method. The microstructure of the as-prepared nanocrystalline metals was characterized by XRD and FESEM. The microhardness and electrical resistivity were tested by the HMV-2 type Microhardness Tester and 6157 type Electrometer, respectively. The synthesis process was also studied. The results show that the spheriform particles in nanocrystalline metals have average grain size of 20–30 nm. The relative density of nanocrystalline Cu, Al, and Ag are 95.1%, 98.1% and 98.3%, respectively. The microhardness of nanocrystalline Cu, Al and Ag are 2.01, 2.11 and 1.26 GPa respectively, which are larger than those of their coarse-grained counterparts by the factor of 4.5, 14, and 2.5, respectively. The electrical resistivity of nanocrystalline Cu at room temperature is 1.5 × 10 −7 Ωm, which is higher than coarse-grained Cu by a factor of 7.5. The pressure is the predominant factor influencing the density of the as-prepared nanocrystalline nonferrous metals.

Recovery of tin from metal powders of waste printed circuit boards

To avoid the adverse effects of tin on the smelting process used to recover copper from metal powders of waste printed circuit boards, an effective process is proposed that selectively extracts tin and its associated metals. That impacts of alkaline pressure oxidation leaching parameters on metal conversion were systematically investigated. The results showed that Sn, Pb, Al and small amounts of Zn in the metal powders were leached out, leaving copper residue. By optimizing the conditions, leaching recovery of 98.2%, 77.6%, 78.3 and 6.8% for Sn, Pb, Al and Zn, respectively, were achieved. Subsequently, more than 99.9% of Pb and Zn in the leaching solution were removed as a mixture of PbS-ZnS in the purification process, which can be used as a raw material in Pb smelting. Approximately 86.2% of Sn in the purified solution was recovered by electrowinning, and the purity of the cathode tin was over 99.8%.

Behavior of silver and lead in selective chlorination leaching process of gold-antimony alloy

Abstract The behavior of silver and lead in the selective chlorination leaching process of gold-antimony alloy was analyzed in detail and appropriate recovery methods were developed. A reduction method by adding gold-antimony alloy powder was adopted to recover silver according to the thermodynamics calculation. The reducing rate of silver can exceed 99% at 80°C for 1.5 h when the dosage of gold-antimony alloy powder is 10%. The dissolution equilibrium curved surfaces of PbSO 4 and PbCl 2 under different conditions were drawn. The experimental results are well consistent with theoretical analysis that indicate lead may be precipitated in the form of lead chloride. The grade of gold in the residue can be further concentrated to 94.5% after being washed with hot water. These two methods have been applied successfully in the practice.

Electrodeposition of Sb(III) in alkaline solutions containing xylitol

Abstract The electrodeposition of antimony in alkaline solutions containing xylitol was investigated using cyclic voltammetry, linear sweep voltammetry and chronoamperometry. The antimony electrodeposition and the chemical stability of xylitol in alkaline solutions were studied by cyclic voltammetric technique. Apparent activation energy, apparent transfer coefficient and exchange current density were obtained by linear sweep voltammetric technique. Initial stages of antimony electrocrystallization were determined by chronoamperometry. Xylitol in alkaline solutions exhibits high chemical stability and there is no redox in solutions when the potential ranges from −1.20 V to +0.60 V (vs Hg/HgO). There is no other redox reaction but hydrolysis occurring on stainless steel in the potential range of −1.75 V to 1.25 V (vs Hg/HgO) while the xylitol decomposition maybe take place on antimony electrode when potential is more negative than −1.70 V (vs Hg/HgO). Cyclic voltammograms with different scan rates indicate that the antimony electrodeposition process is an electrocrystallization which is a completely irreversible electrode process. The apparent activation energy, apparent transfer coefficient and exchange current density were calculated to be 46.33 kJ/mol, 0.64 and 4.40×10−6 A/m2, respectively. The analyses of the chronoamperometric responses support the view of a three-dimensional growth under progressive nucleation. The average diffusion coefficient of antimony was calculated to be 1.53×10−6 cm2/s.