Electrodialysis For Removal And Recovery Of Cr(Ⅵ) From Wastewater

Hexavalent chromium,Cr(â…¥),is toxic,and can act as carcinogens,mutagens,and teratogens.However,Cr(â…¥) is expensive.Thus,it is significant to develop a technique of simultaneous removal and recovery of Cr(â…¥) for environmental pollution abatement and economic purpose.Currently,there are many methods available for the treatment of the wastewater containing ion Cr(â…¥),which have their own advantages.However,none of them can achieve simultaneous removal and recovery of Cr(â…¥) from wastewater.The major objective of this work is to remove and recover Cr(â…¥) efficiently from wastewater using an ED unit with multi baffles and multi stages.In order to investigate the basic performance for wastewater purification,the ED unit developed was operated in batch first.It was revealed that the ED unit with multi baffles and multi stages could treat the wastewater containing Cr(â…¥) efficiently. Concentration of Cr(â…¥) was reduced from the initial 50-150 mg/L to lower than 0.5mg/L under typical conditions.The current efficiency reached 30.9%,and the power consumption was only 2.59kWh/mol Cr(â…¥).With these results above,the ED unit was operated in a continuous mode.The results showed that Cr(â…¥) could be removed and recovered efficiently.After treatment,the concentration of Cr(â…¥) in the dilute effluent decreased from the initial 50-150 mg/L to lower than 0.5mg/L, while the concentration of Cr(â…¥) in the concentrated effluent was higher than 10g/L, with current efficiencies of 4.84-11.45%and power consumptions of 2.24-6.97kWh/mol Cr(â…¥) being obtained.The effects of current,flowrate and initial Cr(â…¥) concentration on the purification efficiency were also investigated,and a simple way to optimize the ED operation was proposed,which used a new concept of charge-mass ratio(CMR).The results showed that the Cr(â…¥) concentration in the effluent was highly dependent on CMR,and there was a optimal value for CMR under which the ED unit could be operated continuously,efficiently,economically and steadily by adjusting the current on the basis of the quality and the flowrate of the wastewater treated.