Research Of Chrome Tanning Sludge Recycling

In the course of leather production, it is a fact that to deal with wastewater containing chromium usually produces chrome tanning sludge, whose contains large amounts of chromium and rich collagen polypeptide materials. Because of this, the chrome tanning sludge as a renewable resoource has great utilization value. The thesis aims at chrome tanning sludge from Zhanhua Industrial Zone,Binzhou, Shandong Province. Through loop method and high temperature roasting method, the trivalent chromium from chrome tanning sludge was extracted for once bathing chrome tannery. Based on the loop method, the collagen peptide in the chrome tanning sludge was extracted after the process of trivalent chromium extracted. The extracted collagen peptide can be applied in paper strengthening agent after modification.The thesis contains the best processes and application of the two kinds method of extracting trivalent chromium in chrome tanning sludge separately.The main contents are as follows:(1) The loop method: The extraction of chromium in the rich chromium sludge was studied to determine the separating agent and extract agent formula.Through the experiment, the best process conditions of separation and extraction of chromium were found out. The extraction Cr2(SO4)3 was applied into a bath chrome tanned in the leather industry. The experimental results showed that: the shrinkage temperature of blue tanned leather was higher than 98℃, and the hand feeling of blue tanned leather was fullness. This provides an effective way for rich chrome sludge recycling.(2) The high temperature roasting method: with muffle furnace, the high temperature can decompose grease and collagen peptide in chrome tanning sludge, liberating chromium from sludge and recycling. The best test conditions are as follows: Heating temperature is 750 ℃, and heat-up time is 3h.Chrome slag immersed in dilute sulphuric acid(p H=2.0), with vaccum suction filtering, it will deserve purified chrome liquid, which recovery rate of chrome over 98%,organic ingredients below 0.2%. The purified chrome liquid was made to be chrome tanning agent to tanning leather whose quality fraction is 3.5%(measured by Cr2O3), whose the shrinkage temperature of blue wet cowhide is greater than98℃, with softness and fulness,and uniform.In the process of paper-pulping, peptide added directly make paper curly and obstructed the intensity of paper.Therefore, it is necessary to modified peptide. The experiment used cationic-type polyacrylamide as modified material,and the modified collagen peptide can increase paper intensity. The main contents of extracting collagen peptide and applying modified collagen peptide on paper strengthing agent as follows:Through the acid-pretreament to chrome tanned sludge, it can separate chrome from sludge effciently; the raw collagen peptide was extracted by the mixture of sodium hydroxide and calcium oxide through the ultrasonic wave assistance. With the toluene to extract collagen peptide,the quantity of Cr2O3 in collagen peptide liquid is lower than 70mg/kg and the content of ashes is lower than 3%, and the extraction yield of collagen peptide can reach 40%. With Polyving akohol as a dispersing agent, collagen peptide liquid(CPL) was modified by cationic polyacrylamide. When the dosage of modified CPL is1.5%(to oven dry stock),it can strength paper tension effeciently. Paper tensile index increased 26.7%, and burst index increased 47.2%.