| Presently, our country is facing tight supply, shortage of mineral resources. However, the waste residues usually contain high content of valuable heavy metals such as zinc, lead and copper, which can easily result in heavy metals pollution and cause damage to humans and environment. Therefore, hydrothermal-sulfidation method was proposed to convert metal contained in the residues to metal sulfides, then recovered by conventional flotation. The recovery of heavy metals from residues not only reduces pollution, but also plays an important role in the environmentally friendly society with the increasingly exhausted natural ores.This study focuses on flotation performance of lime neutralization sludge (LNS) from a Smelt Group treated by hydrothermal sulfidation. Then the microscopic properties between synthesized ZnS and sphalerite were compared, synthesized ZnS was different from natural sphalerite, so crystal size and flotability of ZnS were improved in the process of hydrothermal, which serve for the further recovery of heavy metals from LNS. The results are as follows:(1) Flotation performance of hydrothermal synthesized sulfides by chemical reagents simulating LNS were investigated. The results show that CuS and PbS have a good flotability, the recovery are91%and72.78%respectively, ZnS recovery is28.31%. The microscopic properties of synthesized sulfides were analyzed by XRD, Laser diffraction particle size analyzer and SEM, according to analysis, in respect of crystallinity, crystal size and surface smoothness, CuS and PbS are superior to ZnS. Then the microscopic properties between synthesized ZnS and sphalerite were compared, there was a apparent difference between them. Therefore, the bad flotability of ZnS can be attributed to poor crystallization, small size and rough surface.(2) Flotation behaviors and influence factors of synthesized ZnS from LNS treated by hydrothermal sulfidation were studied. The results illustrate that main mineral composition were gypsum (CaSO4) and sphalerite (ZnS),80%Zn existed in the form of ZnS in sulfidized LNS, only a few ZnS were paragenetic or associated with chalcopyrite (CuFeS2), the fine and amorphous ZnS were flocculated, or sticked on the rhabdoid CaSO4crystals closely. The main factors on zinc flotation were investigated, the results indicated that particle size, temperature and pH were the most important factors on zinc grade, CMC dosage, ultrasonic dispersion and pulp density had effect on zinc recovery. Under the optimal conditions (particle size:400mesh, temperature:60℃, pH value:8, CMC:200g/t, ultrasonic dispersion:30min and pulp density:10%), the grade of zinc concentrate can reach27.4%with a recovery of33.33%. The degree of zinc concentrate can rise up to38%with tailings content of16.3%when one roughing and one concentrating flotation were carried out.(3) Optimal conditions for improving the flotability of ZnS in hydrothermal process were confirmed. The results show that under the condition of5mol/L mineralizer KOH,5%galena,10%precursor Zn(OH)2,260℃of hydrothermal temperature for4h, pure synthesized ZnS recovery increases to82.53%, and the growth kinetcics of ZnS crystal under hydrothermal condititon was found to follow the equation, D769=8.11×1018.t.e(-5756/RT) with an activation ernegy of Ea=57.56kJ/mol. The grade of zinc concentrate in improved LNS can reach31%with a recovery of72.78%, the crystallinity of ZnS is enhanced, crystal size increases to200nm, and the surface of ZnS crystals become smoother. |
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