| The traditional process of heavy metal wastewater treatment represented by chemical precipitation,adsorption,ion exchange and oxidation reduction has made much progress in the research of treatment efficiency improvement and heavy metal recovery,but there are also some shortcomings,such as the difficulty of timely and precise control operating parameters depending on raw water concentration.Especially for the treatment of heavy metal wastewater with high content,many types and large concentration changes of heavy metals such as non-ferrous smelting and washing wastewater and laboratory wastewater,there are problems such as difficulty in timely and accurate adjustment of dosing amount during operation,difficulty in controlling operation conditions and failure of stable standardization of effluent index.Therefore,it is of great significance and practical value to develop a heavy metal wastewater treatment process with convenient operation process,stable treatment effect and easy to realize automatic control.In this paper,we conducted a heavy metal wastewater treatment experiment using a simulated wastewater containing Cr,Ni,Pb and Cu,and investigated the influencing factors such as electrode material,magnetic field strength and direction,current density,initial pH and pole plate spacing.The experimental conditions were optimized by Response Surface Methodollogy(RSM),and the mechanism of heavy metal removal by magnetically enhanced electroflocculation was initially investigated by SEM.The main experimental results are as follows:In the single-factor optimization experiment,the removal efficiency of the reactor with Al-Fe as the cathode was increased by 33%compared with that with Fe-Fe as the cathode;the magnetic field strength of 79 mT in the S-N direction was applied to improve the removal rate by 9.43%;on the premise of satisfying the removal rate and considering the energy consumption,the current density control range was 7 mA/cm2～9 mA/cm2 and the spacing between the electrode plates was taken as When the initial pH value was 6,the removal rates of Ni,Pb and Cu were 99.66%,99.65%and 99.98%,respectively,and the total Cr removal rate was 99%.In the multi-factor optimization experiments,the optimal experimental conditions were obtained after optimization with the help of Response Surface Methodollogy(RSM).When the initial pH was 6.64,the current density was 7.35 mA/cm2,the magnetic field strength was 79 mT,and the reaction time was 26.03 min,the removal rates of several heavy metals reached more than 99.9%and the energy consumption was 91.27(v·mA/cm2·min).The interaction analysis showed that the changes in the removal rates of Ni,Pb and Cu did not remain isotropic for the changes of initial pH,current density,reaction time and magnetic field strength,and the increases and decreases were not consistent.Laboratory wastewater tests containing various heavy metals were conducted under optimized experimental conditions,and the maximum concentrations of Cr,Ni,Cu and Pb in the wastewater were reduced from 80 mg/L,13.6 mg/L,1.8 mg/L and 0.35 mg/L to 0.157 mg/L,0.022 mg/L,0.008 mg/L and 0.001 mg/L,respectively,with removal rates of 99.80%,99.83%,99.55%and 99.71%,respectively.When the concentration of heavy metals in the raw water changed,the removal rate of heavy metals in wastewater could still reach more than 99.55%stably when the reaction time reached the time characteristic value under the optimal working conditions,meeting the requirements for the discharge of a class of pollutants.Compared with conventional electroflocculation,the heavy metal removal rate of magnetically enhanced electroflocculation process is 22.3%higher and the energy consumption is 2.83%lower,and it has good adaptability to the change of raw water concentration.Magnetically-enhanced electroflocculation achieves high efficiency and indiscriminate removal of mixed wastewater with variable concentrations of multiple heavy metals,and proposes a feasible solution for stable standard discharge and automated operation of treatment facilities. |
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