Study On Treatment Technology Of Thallium-containing Wastewater Produced By Electrolytic Zinc Process

Thallium is a highly toxic substances. With the water more and more serious polluted by thallium, water of thallium poisoning are reported in recent years. This study focus on the wastewater containing thallium produced in the process of electrolytic zinc, which use the combination technology of oxidation-sulfide precipitation-flocculation precipitation-adsorption for the laboratory test. The experiment investigates the effect step by step of combination of sodium hypochlorite oxidation, sodium sulfide precipitation, flocculation precipitation and resin absorption treating wastewater containing thallium and determines the optimum process parameters; What is mainly studied in the experiment is the composite flocculant(PSAF-DMDAAC) compounded by polymerization silicate sulfate aluminium and iron and dimethyl diene propyl chloride, and optimizing the preparation conditions. The main conclusions are as follows:(1) It is used the principle of Box-Behnken central composite design to optimize the technological parameter with the combination of the method of sodium hypochlorite oxidation and the method of sodium sulfide precipitation to dealing with the wastewater containing thallium, and the sodium hypochlorite dosing quantity, the sodium sulphide dosing quantity, curing reaction period, the interactive items of sodium hypochlorite dosing quantity and sodium sulphide dosing quantity are all significant impact factor; The optimal experimental conditions of model prediction are as follows: The sodium hypochlorite dosing quantity is 0.6 m L/L, the sodium sulphide dosing quantity is 0.76 g/L, the sulfuration reaction period was 36.72 min. Under the optimal process condition, verifing the result of the experiment: the deviation ratio is 0.17% compared with model prediction results 97.98% while the removal rate of T1 is 97.81% on average.The residual concentration of Tl was 399μg/L.(2) The composite flocculant of PSAF-DMDAAC has the very good effect on flocculation, the optimum technological parameters for preparation PSAF-DMDAAC:(Al + Fe)/Si mole ratio is 2:1, Al/Fe molar ratio is 1:2, DMDAAC dosage is 0.8%, the compounded temperature is 80℃, the removal rate of flocculant to chromaticity, turbidity and Tl in wastewater can reach to 95%, 96.7% and 94.4% respectively in the best preparation conditions; The composite flocculant PSAF-DMDAAC can efficiently remove the thallium in wastewater. The optimum process parameters for removing thallium: initial pH is 9.5, the flocculant dosing quantity is 0.8 g/L, the precipitation time is 15 min. The removal rate of flocculant to chromaticity, turbidity and T1 in wastewater reached to 96%, 96.8% and 96.8% respectively under the optimum technological parameters. The residual concentration of Tl was 18μg/L.(3) The experiment investigates the effect of pH value, temperature, the initial concentration of T1 and adsorption time to resin adsorption, the adsorption experiment of the optimal pH value is 9;The best adsorption temperature is 30℃; Research showed that the resin adsorption T1 achieved the adsorption equilibrium at 80 min, and the resin adsorption T1 conforms to the secondary dynamics adsorption model; The maximum adsorption capacity of resin adsorption Tl is 636.94ug/L, whose adsorption process conforms to monolayer adsorption model; The accumulation of the adsorption quantity is 621.4ug/g reaching to adsorption saturation when using the dynamic adsorption to study resin adsorption Tl; With static adsorption method to study the performance of the resin regeneration. The adsorption rate of resin adsorption T1 remains as high as 95.8% after regeneration 6 times; Dynamic adsorption resin expanded experiment shows that when the experiment device is controled the velocity of 20L/h, the adsorption effect is good, and the Tl concentration in produced water is stable bewteen 2.9μg/L ~3.2μg/L.