The aim is to remove copper from a pyrite cinder by optimizing the chlorination roasting process using response surface methodology (RSM) and the reaction mechanism of chlorination roasting based on thermodynamic calculation was discussed.A quadratic model was suggested by RSM to correlate the key parameters,namely,dosage of chlorinating agent,roasting temperature and roasting time to the copper volatilization ratio.The results indicate that the model is well consistent with the experimental data at a correlation coefficient (R2) of 0.95,and the dosage of chlorinating agent and roasting temperature both have significant effects on the copper volatilization ratio.However,a roasting temperature exceeding 1 170 ℃ decreases the volatilization ratio.The optimum conditions for removing copper from the cinder were identified as chlorinating agent dosage at 5%,roasting temperature at 1 155.10 ℃ and roasting time of 10 min; under such a condition,a copper volatilization ratio of 95.16% was achieved from the cinder.Thermodynamic calculation shows that SiO2 in the pellet plays a key role in the chlorine release from calcium chloride,and the chlorine release reactions cannot occur without it.
LIU JianWEN Shu-mingCHEN YuLIU DanBAI Shao-junWU Dan-dan
The surface properties of sphalerite (ZnS) were theoretically investigated using first principle calculations based on the density functional theory (DFT). DFT results indicate that both the (110) and the (220) surfaces of sphalerite undergo surface atom relaxation after geometry optimization, which results in a considerable distortion of the surface region. In the normal direction, i.e., perpendicular to the surface, S atoms in the first surface layer move outward from the bulk (d_1 ), whereas Zn atoms move toward the bulk (d_2 ), forming an S-enriched surface. The values of these displacements are 0.003 nm for d 1 and 0.021 nm for d_2 on the (110) surface, and 0.002 nm for d 1 and 0.011 nm for d 2 on the (220) surface. Such a relaxation process is visually interpreted through the qualitative analysis of molecular mechanics. X-ray photoelectron spectroscopic (XPS) analysis provides the evidence for the S-enriched surface. A polysulphide (S^(2-)_n ) surface layer with a binding energy of 163.21 eV is formed on the surface of sphalerite after its grinding under ambient atmosphere. This S-enriched surface and the S 2 n surface layer have important influence on the flotation properties of sphalerite.
The type, size, and compositions of fluid inclusions in a natural sphalerite were investigated and the total concentration of Zn released from the fluid inclusions was measured. To compare the total concentration of Zn released from the fluid inclusions with that dissolved from the sphalerite itself, dissolution experiments and theoretical calculations for the dissolution equilibrium of the sphalerite were also performed. The results indicate that large numbers of fluid inclusions with various sizes exist in the sphalerite, which can be divided into four types, i.e., pure gaseous inclusions, pure liquid inclusions, gas-liquid inclusions, and gas-liquid inclusions containing solid minerals. These inclusions were broken open during the grinding process, and their compositions were released to the solution. The total concentration of Zn released from these inclusions reaches 18.35×106mol/L, which is much higher than that of Zn dissolved from the sphalerite itself (1.93×106mol/L) and the theoretical calculation value (2.73×108mol/L).
Shu-ming WenJian LiuBo LiRun-sheng HanYi ZhangJiu-shuai Deng
The electronic structures of three types of lattice defects in pyrites (i.e., As-substituted, Co-substituted, and intercrystalline Au py-rites) were calculated using the density functional theory (DFT). In addition, their band structures, density of states, and difference charge density were studied. The effect of the three types of lattice defects on the pyrite floatability was explored. The calculated results showed that the band-gaps of pyrites with Co-substitution and intercrystalline Au decreased significantly, which favors the oxidation of xanthate to dix-anthogen and the adsorption of dixanthogen during pyrite flotation. The stability of the pyrites increased in the following order: As-substituted < perfect < Co-substituted < intercrystalline Au. Therefore, As-substituted pyrite is easier to be depressed by intensive oxidi-zation compared to perfect pyrite in a strongly alkaline medium. However, Co-substituted and intercrystalline Au pyrites are more difficult to be depressed compared to perfect pyrite. The analysis of the Mulliken bond population and the electron density difference indicates that the covalence characteristic of the S Fe bond is larger compared to the S S bond in perfect pyrite. In addition, the presence of the three types of lattice defects in the pyrite bulk results in an increase in the covalence level of the S Fe bond and a decrease in the covalence level of the S S bond, which affect the natural floatability of the pyrites.
Yong-jun XianShu-ming WenXiu-ming CHenJiu-shuai DengJian Liu
