Dynamics of aluminum leaching from water purification sludge

• Published in: Journal of hazardous materials 2012-05, Vol.217-218, p.149-155
• Main Authors: Cheng, Wen-Po, Fu, Chi-Hua, Chen, Ping-Hung, Yu, Ruey-Fang
• Format: Article
• Language: English
• Subjects: Acidic; activation energy; Aluminum; Aluminum - isolation & purification; aluminum oxide; Dynamic; equations; leaching; mixing; Recovery; Sewage - chemistry; Shrinking core model; silica; sludge; Temperature; Water Purification
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2012.03.007

► The shrinking core model was used for studying the Al(III) leaching from sludge. ► Leaching mechanism conforms to the inert-layer diffusion control. ► The kinetic equation is 1−3(1−x)2/3+2(1−x)=(2707.3exp(−3887.6/T))t. ► Apparent activation energy is estimated to be Ea=32.322kJ/mol. In this investigation, the shrinking core model is used to study the rate of aluminum salt leaching from water purification sludge (WPS). This model, which describes the aluminum leaching rate, can be developed to maximize the Al(III) recovering efficiency. Laboratory results indicate that when the mixing speed exceeds 80rpm, the effect of film diffusion control on the leaching process is greatly reduced, such that any further increase in the mixing speed does not affect the Al(III) leaching rate. Additionally, increasing the temperature or acid concentration improves Al(III) leaching rate. The laboratory data were verified by using the shrinking core model to confirm that the leaching of Al(III) from WPS is consistent with the inert-layer diffusion control model. This finding reveals that large amounts of SiO2, Al2O3 and other inert constituents will form an inter diffusion layer in the WPS and thus become the major limiting factors that control the Al(III) leaching process. The dynamic equation can be expressed as 1−3(1−x)2/3+2(1−x)=(2707.3exp(−3887.6/T))t, in which the apparent activation energy and pre-exponential factors are 32.32kJ/mol and 2707.3min−1, respectively, as determined by solving the Arrhenius equation.