Nickel Residue Handling

Nowadays wastewater from different industries has brought increasing damage to human society, especially heavy metal wastewater, which made the environment and human health greatly suffered. So it is urgent to find effective ways to reduce manifold heavy metals from wastewater before it is dischared into the nature in case it should cause secondary pollution.This paper chose nickel precipitation residue liquor(from Yuanjiang nickel Industry Company in Yunnan province)as object and focused on the operation conditions and effects of two treatment process, ie.ferrite process and neutralization process, to find out a simple but effective way for the removal of heavy metals in the residue.In ferrite process, four influencing process parameters were set, ie.pH, temperature, stirring time and reagents adding ratio. The results showed that the optimum operating conditions were pH value of 11, temperature of 50℃, stirring time of 25min and reagents adding ratio of about 10. After the treatment, heavy metals concentration of the treated residue liquor was lower than that of the national wastewater discharge standard. The sediment from ferrite process can be reused or recycled, which has stable chemical properties, uniform granularity and strong magnetism and is easy to be separated. By comparation the X-ray diffraction pattern and the spinel ferrite Fe3O4 diffraction pattern, it can be seen that the magnetic part of the sediments has crystal structure of the spinel ferrites. However, ferrite process has some deficiencies, such as warmming difficulties, comsumption of ferric salt, caustic soda and heat energy, long processing time and higher processing costs.In neutralization process, two processes were compared. In one process,5% lime was put into the residue liquor to regulate its pH value to about 9.5 firstly. Then after precipitation and filtration, put lime into the supernatant to regulate its pH value to be about 12.5. In the other process, put 5% lime into wastewater to regulate its pH value to be about 12.5. After precipitation and filtration, put polymeric ferric sulfate (PFS) into supernatant to regulate its pH value to be about 8.5. At the same time, the impact of refluent sludge and the refluent way were studied. The results showed that the concentration of the heavy metals of the treated residue liquor was lower than that of the national wastewater discharge standard. For the first process, firstly alkalizing the sludge and then neutralizing is better than firstly acidulating sludge and then neutralizing, and the optimum volume of refluent sludge is 40% and 50%. But the pH value of the treated residue liquor is higher, and it can not be discharged directly. For the second process, the optimum volume of refluent sludge is 30%-40%, and the pH value of the treated residue liquor is about 8. So it can be discharged directly. Compared with processes without sludge refluece, the sludge moisture of the sludge refluence process decreased from 93.27% to 90.81%, resulting that:the sludge volume was reduced by 1/4; the sedimentation rate was more efficient; the processes was more efficient and reduced the reagent consuming as well.Through the comparation of the ferrite process and the neutralization process, it's concluded that sludge recycling-lime neutralization-PFS process is the optimum process for the nickel precipitation residue liquor. It's simple, easy-operation, cheaper and adapt to the wastewater from nickel smelter. At the same time, some advices were gived for treating sludge.