Reserch On Steadying Heavy Metals In The Sludge By Ferrite Process

The sludge, which has produced in the industrial wastewater treatment process, oftencontains a number of heavy metals. Because the heavy meatals have characteristics ofbiodegradable and easily accumulated this is different from the characteristics of the commonpollutants, if the heavy metals in the sludge is unstable and re-enter the environment, it willcause secondary pollution. The ferrite process is a simple, economical and efficient sewagetreatment process; the ferrite sediment is chemically stable, and could be separated andrecovered, then be used as a magnetic material. Therefore, in this study, ferrite process is usedto stabilize the heavy metals in the sludge, and the the process reaction conditions and effectsare discussed.This study used three different chemical dosing ways to provided iron ions forconstituting the ferrite: separately dosing Fe²⁺ orFe³⁺, dosing both Fe²⁺and Fe³⁺or dosingFe²⁺and H₂O₂. The results show that, stabilizing the heavy metals has good effect by thechemical dosing ways of dosing both Fe²⁺and Fe³⁺and dosing Fe²⁺and H₂O₂, and the effectof the first one is better than the effect of the second, the stabilizing effect of heavy metals, byseparately dosing Fe²⁺or Fe³⁺, is slightly worse.In this research, ferrite is used to stabilize Ni and Cr in the sludge, in order to explore themain factors in the process, then determine the optimum conditions. The main influencingfactors including: the value of n (Fe³⁺)/n (Fe²⁺) when dosing Fe²⁺and Fe³⁺; the value ofn (Fe²⁺)/n （H₂O₂） when dosing Fe²⁺and H₂O₂; the dosing ratio; pH; temperature and stirringtime. The results show: the right proportion of Fe³⁺and Fe²⁺must be choosen, in order toeffectively promote Ni2+or Cr3+and Fe²⁺, Fe³⁺to generate stable ferrite, excessive Fe³⁺orFe²⁺is not conducive for the formation of ferrite. The dosage were highly positive correlationwith the steady-state content of Ni and Cr, in another word, the greater the dosage is, the moreheavy metals entering into the ferrite lattice is. Meanwhile, the steady state content of Ni andCr increases firstly and then decreases slowly as the pH value increases, the pH in the weaklyalkaline range is the most suitable for the generation of ferrite. Certain temperature will leadheavy metals in the sludge transforming into ferrite, but a large number of Fe²⁺wouldtransform into Fe³⁺when the temperature is too high, the formation of ferrite is hinderedwhen Fe²⁺is insufficient. After heat and stir for some time, more than60%of Ni and90%of Cr in the sludge transformes into a stable state, the results show that the heavy metals in thesludge stabilized by Ferrite is efficient.This study demonstrates that Ferrite stabilizing heavy metals in the sludge process issimple, efficient, and ferrite generated has the value of recycling, so Ferrite is a practical process to make the heavy metals in the sludge stabilization, then the study determine theoptimum conditions and technical parameters.