Study On The Purification Of Arsenic Wastewater With High Iron Concentration And The Preparation Of Composite Salt Flocculant

The waste water from the zinc smelter with high iron concentration in Inner Mongolia was researched in the paper.The wastewater was purified by two-step reduction method and the purification mechanism was analysed.And the purified wastewater was used as raw material,the preparation process of polyferric sulfate zinc composite salt flocculant(PFSZ)was developed.The preparation performance was studied by the reaction conditions experiment and the response surface method.The metal balance and the cost of the chemical process and the PFSZ preparation process were calculated,and the source distribution of iron and zinc in the PFSZ product was obtained.According to GB-14591-2016,the product indexes were tested.It was analyzed by SEM,XRD and FT-IR.The performance of PFS and PFSZ on paper mill wastewater was correspondingly studied.The theoretical basis and practical application value were provided for the preparation of PFSZ which from zinc smelting wastewater.The concentration of TFe,Zn2+and SO42-was high,and a certain amount of Cu2+,As3+ and Cd2+ impurities was contained in the wastewater.The reduction of wastewater was carried out by one-step reduction method and two-step reduction method.The agent cost can be greatly reduced by two-step reduction method compared with one-step reduction method.The optimal experimental conditions for purification were:the addition of iron powder reaction for 0.5 h,and then the addition of zinc powder for 1 h,the addition amount of iron powder and zinc powder were 0.7%(m/v),0.4%(m/v)respectively,the reaction temperature of 40 ?,and the stirring speed of 800 r/min.Under these conditions,the removal rates of As3+,Cu2+ and Cd2+ can be reached 99.99%.The concentrations of TFe,Zn2+ and SO42-in the purified solution were 33.52 g/L,9.57 g/L and 92.62 g/L,respectively.The mechanism of the purification reaction is revealed by the principle of standard reduction electrode potential at normal temperature.The process for the preparation of PFSZ by purified wastewater was developed.Due to the high turbidity of kaolin simulated wastewater,the performance of the flocculant was measured by the kaolin simulated wastewater removal rate.The optimum conditions for preparation were:pH of 2.0,H2O2 as oxidant,the addtion of 5%(v/v),SO42-[Zn+Fe]of 1.35,temperature of 60 ? and curing time of 2 h.The turbidity removal rate of kaolin simulated wastewater by this condition can be reached 98.94%.The priority of impact factors affecting the turbidity removal rate of kaolin is:the addition amount of oxidant>pH value>SO42-/[Zn+Fe]ratio.The source distribution of iron and zinc in the PFSZ product was obtained.41.5%and 54.74%of the iron and zinc are derived from initial wastewater,and 12.02%and 39.53%are respectively derived from the powder dissolved in the purification process.The relative error of iron and zinc metal balance in the purification process was 1.20%and 0.94%,respectively.In the process of preparing PFSZ,the relative error of iron and zinc metal balance was 1.32%and 1.99%.In the overall process,The relative error of iron and zinc metal balance was 4.54%and 6.08%,respectively.According to the GB-14591-2016 standard,the indexes of the flocculant products were tested,and the flocculant product was qualified,which can be used for the treatment of industrial water.The results of SEM,FT-IR and XRD showed that the PFSZ particles were non-spherical,and the absorption peaks of PFSZ were-OH,Fe-OH,Fe-O and Zn-O,the phase of the flocculant was Fe2(SO4)2(OH)5(H2O).The comprehensive analysis showed that the prepared flocculant product was[(Fe,Zn)(OH)n(SO4)3-n/2].The PFSZ has good flocculation effect on paper mill wastewater.The best flocculation effect can be obtained under the condition of pH 6.0,flocculant dosage 200 mg/L and temperature 45 ?.The turbidity rate can be reached 65.0%and 95.2%,respectively.What's more,the PFSZ has better flocculation effect on paper mill wastewater than the commercially available PFS.This is due to the synergistic effect of Fe3+and Zn2+in the flocculant,and the flocculation ability of composite salt flocculant was better than single flocculant.