Removal of heavy metals from stainless steel surface treatment wastewater by electrodialysis process

Abstract

In this research, the removal of iron ions from stainless steel surface treatment wastewater using electrodialysis process in batch mode operation was studied. In batch mode operation, several operational conditions such as electric potential, initial acid concentration and other elements in the wastewater were also investigated. The results found that high electric potential the period of the removal of metals ions were increased. As various applied electric potentials were studied, the flow rate might have influenced the transportation of ions. The ions could be faster transported through the membrane at faster flow rate than at slower flow rate. At the electric potential of 5.0 v, about 98% of the fe2+could be removed within 2 hours. The initial acid concentration had affected with the removal iron ion. At the high initial acid concentration, the period of the removal of iron ion was increased. The presence of other heavy metals ions in the wastewater was not much affected the removal of iron ion due to it was present in very little amount. Furthermore, the current efficiency was decreased and the specific power consumption (spc) was increased in the removal of fe2+ when the amount of ions was increased. Finally, the removal of fe2+, ni2+ and cr3+ in real wastewater in batch mode was studied. The concentrations of fe2+, ni2+ and cr3+ after treated by the electrodialysis process were 4.33, 0.03 and 0.09 mg l-1 respectively which were lower than those allowed by the industrial effluent standard regulated by the department of environmental quality promotion. However, the ph value was lower than the allowed by the industrial effluent standard. Thus, it could not be released to the environment but reused or recycled as a makeup feed in the metal surface treatment process and the production cost could be reduced.