A Study On Separation Of Heavy Metals From Sludge By Coupling Pulsed Ultrasound And Hydrodynamic Cavitation

With deteriorated impacts on environment, heavy metals sludge attracted more and moreattention at home and abroad, but it is a technique problem to recycle heavy metals withhigher value from sludge. This paper provided a novel heavy metals sludge treatment bycoupling the pulse ultrasound and hydrodynamic cavitation.According to leaching rate and content percentage of metals in solid, we investigatedimpacts of the initial p H, ultrasonic generator power, the length of orifice plate, diameter oforifice on lab-prepared synthesized metal bearing sludge. Then, the optimal conditions wereselected to deal with industrial sludge which contained much more complicated components.It demonstrated that, with the operation conditions optimized at initial p H of 3.0,ultrasonic generator power of 48.84 W, the length of orifice plate of 15 cm, diameter of orificeof 2 mm, the PUS-HD process showed a superior performance over the others(theconventional US-HD and original HD). As for lab-prepared sludge, which consists Cu(OH)2and Fe(OH)3, Cu content in solid reduced from 11.3% to 0.350 %, and its leaching rateincreased from 79.3 % to 99.5 %; and Fe content increased from 43.3% to 52.1 %. In terms ofindustrial sludge, it contained more components, such as 26.81 % of Fe, 11.28 % of Cu,0.045 % of Ni and 0.019 % of Cr, after acid-leaching treatment and PUS-HD cavitation, Cucontent reduced to 0.038 %, and its leaching rate reached 99.7 %; Ni reduced to 0.058 ×10-2 % and its leaching rate was 99.5 %, while Fe was 24.1 % and its leaching rate only1.60 %, Cr was 0.012 % and its leaching rate was 27.8 %. They have been separatedeffectively by PUS-HD.In a word, PUS-HD was considered as an effective treatment for heavy metal sludge,which made a theoretical foundation for soil remediation and suggested a great potential inenvironmental protection.