| Zinc anode slime, a kind of residue produced in the process of zinc electrowinning, is a secondary resource abundant in manganese, lead and silver etc. The present method treating this residue in zinc ectrowinning plants is to return it to the leaching operation as an oxidant. It works well in reuse of manganese by not changing Mn(IV) to Mn(II), but fails to recycle lead and silver efficiently as early as possible. And there is no feasible and efficient technology till now which has done well in both of these two aspects. In this thesis, a combined beneficiation technology, including flotation, magnetic separation and gravity separation, to realize the separation of manganese, lead and silver, was developed based on the physicochemical property research. The electrochemical atmosphere background produced by Mn(IV) and Mn2+in the acidic pulp of this residue and its influence on the occurrence of lead, silver as well as thiol collectors were determined with a themodynamic method. The interaction mechanism of the of thiol collectors with lead and silver minerals in the pulp was investigated by means of infrared spectroscopic analysis, quantum chemical calculation and other research methods. The main research contents and innovations are as follows:(1) Physicochemical properties of zinc anode slime and technology for comprehensive recovery of manganese, lead and silver minerals.Zinc anode slime contains such major valuable elements as manganese, lead and silver, of which the main existing forms of metalliferous minerals are cryptomelane (KMn8O16) for Mn, anglesite (PbSO4) for Pb, and kerargyrite (AgCl), silver oxide (Ag2O3) and silver oxy-salt of nitrate (Ag7NO11) for Ag. The pulp of zinc anode slime is weakly acid, with pH below5, and the concentration of Mn2+is5.8×10-2mol.L-1.Thiol collectors could only recover silver minerals from zinc anode slime. Flotation by xanthate after sulfidation could not recover anglesite from zinc anode slime. The combined flowsheet of "flotation-magnetic separation-gravity separation" performed very well to separate minerals of manganese, lead and silver respectively. By applying this technology, a silver concentrate with high silver grade,48515g/t, an anglesite concentrate containing lead60.89%, and a manganese concentrate with50.17%manganese could be obtained from zinc anode slime with grade of manganese, lead and silver being37.48%,21.54%and1628g/t, respectively. The total recovery of lead and silver in the lead and silver concentrates reached84.78%and74.71%respectively, and the manganese recovery is91.86%.(2)Thermodynamic analysis of the pulp system of zinc anode mudThe Eh-pH diagrams for different systems have been drawn according to the themodynamically calculated data, based on which the background pulp potential of zinc anode slime and its influence on the occurrence of lead and silver components, the existing state of thiol collectors as well as the flotation of anglesite by xanthate after sulfidation, have been discussed. The results indicate that the pulp potential of zinc anode slime is mainly controlled by the MnO2, the concentration of Mn2+and the pH in the pulp, thus forming a strong oxidation atmosphere which called the background pulp potential of zinc anode slime. In this strong oxidation background pulp potential, lead mainly occurred as anglesite, silver can occurred as Ag, Ag2O, AgCl, AgO, Ag2O3, etc. The themodynamically stable products of sulfur in the pulp is not S2-, HS-, or S0, but SO42-, demonstrating that the sulfidation of anglesite by Na2S or NaHS cannot be achieved; The thermodynamically stable products of thiol collectors in zinc anode slime pulp are their corresponding oxidized dipolymers.(3) The flotation behavior of lead and silver minerals in the pulp of zinc anode slimeMicroflotation tests for pure minerals of anglesite and kerargyrite indicated that these two minerals have good floatability with thiol collectors such as xanthate and aerofloat, on the pH range of3-7. In the presence of MnO2, the floatability of kerargyrite maintains well but that of anglesite turns worse. Dixanthogen and bis-aerofloat have strong collecting ability to kerargyrite comparing with worse collecting ability to anglesite in the presence of SO42-. The infrared spectrum tests verified the selective adsorption of dixanthogen and bis-aerofloat on the surface of kerargyrite in the presence of SO42-.(4) Mechanism of the selective adsorption of thiol collector oxidized dipolymers on the surface of silver containing minerals in zinc anode slime.The highest occupied molecular orbit (HOMO) energy and the lowest unoccupied molecular orbit (LUMO) energy of Mn4+、Pb2+、Ag+have been calculated according to the ionization potential and electron affinity of element. The HOMO and LUMO energy of thiol collector oxidized dipolymers have been also calculated according to PM6in semiempirical quantum mechanics method. It’s clearly shown by comparing the LUMO energy of Mn4+、Pb2+、Ag+with the HOMO energy of thiol collector oxidized dipolymers that the latter was close to the LUMO energy of Ag+, indicating that the covalent coordinated chemisorption of those thiol collector oxidized dipolymers on Ag+is prone to happen.The changes of interaction energy between four kinds of mineral crystals (kerargyrite, silver oxide, anglesite and cryptomelane) and a variety of adsorbents (dixanthogen, bis-aerofloat, bis-diethyl dithiocarbamate, H2O, OH-, Cl-, SO42-) have been calculated by Material Studio(Adsorption Locater module). The results indicate that thiol collector oxidized dipolymers could not be adsorbed on the surface of cryptomelane. These thiol collector oxidized dipolymers could be adsorbed on the surface of anglesite, kerargyrite and silver oxide in the absence of SO42-. With the existence of SO42-, these collectors could only be adsorbed on the surface of silver minerals, due to the competive adsorption of SO42-on the surface of anglesite. |
PDF Full Text Request