Extraction kinetics of heavy metal-containing sludge

• Published in: Journal of hazardous materials Vol. 123; no. 1; pp. 112 - 119
• Main Authors: Lee, I.-Hsien, Wang, Yi-Jing, Chern, Jia-Ming
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 31.08.2005; Elsevier
• Subjects: Applied sciences; Chemical engineering; Citric Acid - chemistry; Crystallization, leaching, miscellaneous separations; Exact sciences and technology; Extraction; Extraction and Processing Industry - methods; General purification processes; Heavy metal; Kinetics; Leaching; Metals, Heavy - chemistry; Models, Chemical; Nitric Acid - chemistry; Particle Size; Pollution; Reactors; Sewage - chemistry; Sludge; Temperature; Wastewaters; Water treatment and pollution; Extraction; Kinetics; Sludge; Leaching; Heavy metal; Agitation; Particle size; Extract; Modeling; Transport process; Batchwise; Electrodeposition; Lixiviation; Diffusion; Reactor; Activation energy; Extraction agent; Extraction process; Metallurgical industry; Empirical model; Nitric acid; Kinetic model; Chemical reaction; Trend analysis; Thermodynamic properties; Waste water purification
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2005.03.035

In order to remove and recover copper, zinc, cadmium, and chromium from the wastewater treatment sludge generated by an electroplating process, the heavy metal extraction kinetics was studied in a batch reactor using two different extraction agents (nitric and citric acid) at constant agitation speed (150 rpm) and solid to liquid ratio (10 g/L), but varying acid concentrations (0.02–0.10N), temperatures (25–85 °C in nitric acid solution, 25–95 °C in citric acid solution), and sludge particle sizes. The shrinking-core model and empirical kinetic model were adopted to analyze the experimental data. Although both models could fit the experimental kinetic data well, the obtained parameters of the shrinking-core model did not show reasonable trends varying with the experimental variables while the empirical model parameters showed significant trends. The experimental and modeling results showed that the metal extraction rates increased with acid concentration, temperature, but decreased with increasing particle size. Nitric acid was found to be more effective than citric acid to extract the heavy metals from the sludge. The extraction activation energies obtained in this study suggested that both a physical diffusion process and a chemical reaction process might play important roles in the overall extraction process.