Deactivation Of Heavy Metals In Sludge By Purified Attapulgite

With the increasing of urban sewage, the continuous improvement of the treatmentfacilities as well as the deepening processing degree, the sludge is continuous increasing inrecent years. As sludge contains nutrition elements which are indispensable for plant growth,such as N, P, K, etc., so the farm application of sludge is an important way for sustainableutilization of sludge resources and improving soil fertility. But the heavy metals which sludgecontains will migrate into the soil, they can affect the normal growth of crops, and mayendanger human life and health through direct contact and the food chain. So the heavymetals affect the value of the sludge utilization. Bioactivity and mobility of heavy metals notonly depend on the total amount, to a great extent, depend on heavy metal forms. Therefore, itis attracting more focus of passivating the heavy metals in sludge, because it can reducebiological effectiveness, activity and minimize the risk of heavy metals.The raw material which was dehydration sludge in the paper was from LanzhouQilihe-aning sewage treatment plant. The passivation agent was purified red attapulgite claywhich was from Gansu Jingyuan. The dehydration sludge and purified red attapulgite claymixed together by different appending proportion. The experiment studied the pH, EC, thetotal amount, water soluble state, DTPA extraction state of the four kinds of heavy metals(Cu,Ni, Cd, Zn). The distribution of the heavy metal forms of BCR sequential extraction and theecological toxicity of the heavy metals were also studied. The effect of the effectiveness ofthe heavy metals which purified attapulgite impacted on the sludge was analysed by varivanceanalysis and multiple comparision.The main conclusions are as follows:(1) In purified attapulgite, the purity and the specific surface area of attapulgite wereimproved.(2) The content order of four kinds of heavy metals was Zn>Cu>Cr>Ni in dehydrationsludge. The form distribution of Cu, Ni and Cr were F4>F3>F1>F2, the form distribution ofZn was F4>F3>F2>F1. Cu and Ni mainly existed in unstable state, Cr and Zn mainly existedin steady state.(3) With the increasing of the proportion of attapulgite, the pH value increased at thesame time. With the extending of the mixing time, the pH value decreased at the sameproportion of attapulgite. With the increasing of the proportion of attapulgite, the EC valuedecreased at0day. With the increasing of the proportion of attapulgite, the EC valueincreased at the other days. With the extending of the mixing time, the EC value changed veryslightly all the time at the control treatment, the EC value presented the tendency of risingfirst and declining then at the other treatments.(4) Increasing the proportion of attapulgite and extending the mixing time caused thereducing the content of the water soluble state. Increasing the proportion of attapulgite and extending the mixing time could promote the decreasing of DTPA extraction state of Ni andZn. Increasing the proportion of attapulgite could promote the decreasing of DTPA extractionstate of Cu and Cr, but extending the mixing time could promote the increasing of DTPAextraction state of Cu and Cr.(5) At the same time, increasing the proportion of attapulgite could promote thetransformation of forms of F1, F2and F3to F4of Cu and Ni, F1, F2and F4to F3of Cr, F1,F3to F4and F3of Zn.(6) For Cu and Ni, increasing the proportion of attapulgite reduced the mobility andcaused the active form transformating to the stable form at the same mixing time, extendingthe mixing time increased the mobility and caused the stable form transformating to the activeform at the same proportion of attapulgite. For Cr, increasing the proportion of attapulgite andextending the mixing time increased the mobility and caused the stable form transformating tothe active form. For Zn, increasing the proportion of attapulgite and extending the mixingtime reduced the mobility and caused the active form transformating to the stable form.(7) Increasing the proportion of attapulgite and extending the mixing time caused thereducing of the ecological toxicity of heavy metals.