Research On A Mechanical Agitation Induced Crystallization Process For The Removal Of Copper In Water

The background of this study included two aspects.One was that the copper concentration in the effluent of precipitation of cuprous chloride for the removal of radioactive iodine from the water in our research group was around 20 mg/L,it could not satisfy the Sanitary Standard for Drinking Water Quality（GB 5749-2006）and need to be further purified.Additionally,in the metal smelting industry and manufacturing activities,there are a large number of copper containing wastewater needs to be treated before discharged.This study based on the principle of induced crystallization precipitation,copper carbonate was used as seed crystal with the dosage of 1 g/L,sodium carbonate was used as precipitant.In the jar test,the optimal sodium carbonate dosage was selected through the tests of nine different dosages,the initial copper concentration was around25 mg/L in these tests,when the molar ratio of CO₃^2-and Cu²⁺was 3.14,the copper removal rate reached 99.5%and the volume of precipitates was small.Additionally,the reaction time had little effect on the test results when it was larger than 5 min,the precipitation time should not less than 8 min,the best mixing strength should keep the velocity gradient at 88 s^-1.The mechanical agitation microfiltration process was employed in the treatment of the copper effluent of the precipitation of cuprous chloride for the removal of radioactive iodine,the dosage of sodium carbonate was accordance with it in the jar test of the same molar ratio.The results indicates that,the turbidity and the copper concentration of the effluent were all satisfied the standards.However,the effluent copper concentration was unstable,as a results,abundance of Cu（OH）₂ flocs generated due to the excessive CO₃^2-,it lead to the clogging of the sand filter and the back flush frequency of the sand filter was 4 times/day.The mechanical agitation microfiltration process was used in two level of copper concentration,when the initial copper concentration was around 20 mg/L,the dosage of sodium carbonate was 104 mg/L which accordance with the molar ratio in the jar test.In the two tests,the removal efficiency were all higher than 96%.Additionally,the SF declined to 57%of the initial SF.1900 L copper dissolved raw water was treated and the volume of the precipitate generated in the two tests were 570 mL and248 mL respectively,the effective concentration of copper was realized in the two tests.In the study of high initial copper concentration treatment,three tests were completed based on about 50 mg/L initial copper concentration,and the dosage of sodium carbonate were 140 mg/L,160 mg/L and 180 mg/L,914 L copper dissolved water was treated.The results indicated that,the dosage of sodium carbonate 140mg/L was inefficient to keep the effluent copper concentration below 1 mg/L.Due to the generation of the incompact flocs,the concentration factors of these three tests were all lower than that of the tests based on about 20 mg/L copper concentration.It indicated that,keeping the residual CO₃^2-concentration around 55 mg/L could ensure the copper concentration of the effluent below 1.0 mg/L,simultaneously,keep the value of saturation index lower than 3.17 could make sure the precipitate grew well in crystal form so that a high CF value could be reached.A low saturation index value could be realized by adding precipitant slowly.