Research On The Treatment Of Lead-zinc Sulfide Flotation Wastewater By Chemical Oxidation

Flotation is the most commonly used ore dressing method in sulphur lead-zinc sulfide mine, in order to separate valuable metals such as lead and zinc effectively, organic thiochelate collector need to be add in flotation process, such as Xanthate (alkyl carbonate disulfide generation), Ethyl thiocarbamate (sodium diethyldithiocarbamate) and Aniline aerofloat (dianilino dithiophosphoric acid), etc. Among them, Aniline aerofloat is hard to decompose spontaneously. Except part of these organic thiochelate collectors react with sulphur lead-zinc sulfide mine, the others are residues in flotation wastewater, thus caused a high COD value in it. These gathering of streams of flotation wastewater go to tailings, caused a high chemical oxygen demand (COD is about70-120mg/L),and makes it hard to meet the discharge standards unless purificationtreatment.Firstly, the effect of oxidizing agents (H2O2, NaClO and Na2S2O8) to remove COD (70～90mg/L) of the tailing discharge wastewater from sulphur lead-zinc mine was compared. The results demonstrated that:(1) only by H2O2(no adjust pH, no add Fe2+) can hardly remove COD of the tailing discharge wastewater;(2) the optimal test conditions were100-125g/t of NaClO,0.8%of alkalinity,60r/min of stirring intensity and40min of reaction time, the COD of wastewater could reduce from about90mg/L to50mg/L;(3) the optimal test conditions were100g/t of Na2S2O8,60r/min of tiring intensity, stir for3min, then40min of retention time, the COD of wastewater could reduce to about45mg/L, however, the test results need for further research.Next, the effect of NaClO to remove high COD(90-120mg/L) of flotation wastewater was compared, this wastewater was mixed of tailings reservoir wastewater and (?)30m thickener overflow effluent (6:4). The results demonstrated that:(1) the effect of high alkalinity (about1%) NaClO is much better than low alkalinity (about0.5%) NaClO;(2) the optimal test conditions were150g/t of high alkalinity NaClO, this process could reduce the COD of wastewater to about50mg/L.Finally, the mechanism of degradation Aniline aerofloat wastewater by NaClO was discussed. The results showed by single factor and orthogonal experiments were:higher removal rate of Aniline aerofloat with the increase of concentration of oxidant, when the concentration of Aniline aerofloat wastewater was100mg/L, the concentration of oxidant was8.8g/L, the removal rate of Aniline aerofloat could reach95%, the COD of Aniline aerofloat wastewater could reduce from130mg/L to about70mg/L. The removal of Aniline aerofloat (with its molecular fomula (C6H5NH)2PSSH) has been investigated by using NaClO as oxidizer and the reaction products were analyzed by HPLC. The results showed that free radical formed by NaClO in the water could attack two aniline two phosphorothioate molecule, and Aniline aerofloat degradation follows the steps as follows: first breaks the chemical bond between N and P, organiccompounds of benzene ring had a substitution reaction with Cl-in the water quickly, and formed three isomers which are: o-chloroaniline, m-chloroaniline and p-chloroaniline, then the element S in the dithiophosphate functional group was oxidized to sulphate with high valence gradually.