|| Ferrite process (denoted by FP) has been used for treating the waste-liquid containing heavy metal for many years. Related researches have shown that this method could catch the heavy metal regulated by environmental law into the structure of spinel, and sludge from FP also conformed the standards of toxicity characteristic leaching procedure in EPA of Taiwan. On comparing with neutral precipitation of conventional method, spinel’s sludge produced in FP had an ease separation of solid-liquid and no need of solidification in further treatment. These spinel, belonged to the magnetic material, could be used for applications such as brick of blinder guide, magnetic symbol, absorber of electric wave and adsorbent. Therefore, this method has a great potential for treating the waste containing heavy metal in laboratory. |
This study was to investigate the optima conditions in removal of heavy metal in waste liquid in laboratory by using the FP of conventional, two and three stage. All experiments, including one ion and ten ions heavy metal mixed in a solution, were conducted in a batch- type reactor for total concentration of 2000 mg/L heavy metals. The major parameters included temperature, ferric ion dosage, aeration intensity and pH. The performance of treatment in FP was judging by that the concentration of all heavy metals in filtered solution and the heavy metal containing in sediment sludge should be below the regulations of effluent standards and TCLP standards.
In conventional one stage of FP experiments performed at constant temperature and pH, the residual concentration of heavy metals in filtered solution was below the effluent standards except of Cd and of Hg; in results of TCLP showed that higher dissolvion of Cd, Cu and Pb leached from sediment and the rest ions of heavy metal passed the regulations. Thus, we conducted individually for Cd, Cu and Pb to find the optimal conditions. The optimal pH of 7 and temperature above 70 ℃ for Cd and Pb and the optimal pH of 10 and temperature above 80 ℃ for Cu were obtained. They were be used for combination of process in various stage to achieve the goal of treatment performance.
After the combination of two and three stage reactions, three stage reactions in series was the only selection in removal of ten heavy metals performed by FP. As a result, the sequences were in the following: (1) 70℃, pH=9 (2) 90℃, pH=9 (3) 80℃, pH =10 , and the reaction period was 40 min for each stage.