| Abstract:The shortage of resources and the environment pollution have ciritcally restricted the development of social economy. It is great significance to alleviate the shortage of resources and reduce the pollution of the environment by the research on the treatment and resource reoverying technology of heavy metal-containing sludge. Using hydrothermal sulfidation to deal with wastes containing heavy metal not only makes heavy metal converted into metal sulfide that is easier to float, but also makes the wastes more stable after treatment. So it can synchronously trnasform wastes into resource and make the wastes harmless.This paper focuses on the recovery of zinc in the lime neutralization sludge which is produced in the process of smelting waste water management. The effect of calcium in the process of hydrothermal sulfidation was studied, especially the phase transformation process of calcium and zinc, the law of crystal growth, as well as their speciation state. The influence mechanism of the existence of calcium on the flotation of zinc sulfide was investigated by single minerial flotation test, Zeta potential test, infraed spectroscopic analysis and adsorption test. In order to promote the recovery of zinc, the hydrothermal crystal modification technology was performed and the optimum parameters of the hydrothermal sulfidation were determined. The optimization experiment of hydration modification was also carried out to prompt the recovery of zinc. The main results were as following:(1) The study on the influence of calcium on the hydrothermal sulfidation and flotation showed that when Zn(OH)2and S reacted under the hydrothermal condition, the sulfide rate of zinc was only30.27%, while in the presence of calcium, the sulfide rate was as high as86.89%. It indicated that calcium was beneficial to the disproportionation reaction of sulfur, and thus promoting the hydrothermal sulfidation. Calcium sulphate single mineral flotation test showed that the flotation recovery rate of CaSO4was only26.17%with butyl xanthate or DDTC as collector. The experimental results of infrared spectrum analysis and adsorption test further showed that the calcium sulfate did not exert competition on the adsorption of collector in the process of flotation. The zinc sulfide generated in the hydrothermal sulfidation process was tiny, and seriously adhere on the surface of calcium sulfate. It was hardly to separate them in the flotaion process, and result in relatively low flotation recovery of zinc sulfide.(2) The optimum parameters in the hydrothermal crystal modification are established as following:the liquid-solid ratio:3:1, the precursor concentration:15%, the molar ratio of zinc and sufur(Zn/S):1:1.2. The result showed that adopting the hydrothermal crystal modification, the crystal size of zinc sulfide increased to about200-300nm, with dense structure and smooth surface. Also the adhesion phenomenon was considerably reduced. The flotation results showed that the recovery rate of zinc from the sludge increased from22.51%to45.34%, while the enrichment ratio increased from1.3to1.6.(3) The research of hydration technique showed that with10%Na2SO4as activator, a hydration temperature of100℃, a hydration time of1h, and0.5%CaSO4·2H2O crystal(-75um) as crystal seeds, small calcium sulphate crystal was transform into significantly lager dihydrate calcium sulphate crystal. Most of the particles were500microns, with prismatic shape and smooth crystal surface. The neutralization sludge which had been treated by hydrothermal sulfidation was used to conduct the hydration experiment, and the product was screened. Flotation test was performed with the undersize materials. The result showed that the recovery rate of zinc was64%, while the concentrate grade was34%. |
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