Mercury adsorption on granular activated carbon in aqueous solutions containing nitrates and chlorides

• Published in: Journal of hazardous materials 2011-09, Vol.192 (3), p.1842-1850
• Main Authors: Di Natale, F., Erto, A., Lancia, A., Musmarra, D.
• Format: Article
• Language: English
• Subjects: Activated carbon; Adsorption; anions; Applied sciences; Aqueous solutions; Biological and physicochemical phenomena; Carbon - analysis; Chemical engineering; chemical speciation; Chemistry Techniques, Analytical; Chlorides; Chlorides - chemistry; Exact sciences and technology; Hydrogen-Ion Concentration; Ion speciation; Ions; Mathematical models; Mercury; Mercury - analysis; Mercury adsorption; Model aqueous solution; Natural water pollution; nitrates; Nitrates - chemistry; Pollution; Speciation; Temperature; Water - chemistry; Water Pollutants, Chemical - analysis; Water Purification - methods; Water treatment and pollution; working conditions
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2011.07.021

► Mercury adsorption on GAC was studied on model aqueous solutions at different pH, temperature and concentration of mercury species. ► Experiments supported a speciation analysis aimed at determining correlations between adsorption capacity and concentration of specific mercury ions. ► Mercury adsorption depends on cationic species, while anions contributions occur for basic pH. Speciation explains effects of investigated parameters. ► The effect of temperature is satisfactory explained by process exothermicity and mercury speciation. ► A modification of original material occurred during tests with hydrochloric acid at pH 2 and 45 and 55 °C. Adsorption is an effective process to remove mercury from polluted waters. In spite of the great number of experiments on this subject, the assessment of the optimal working conditions for industrial processes is suffering the lack of reliable models to describe the main adsorption mechanisms. This paper presents a critical analysis of mercury adsorption on an activated carbon, based on the use of chemical speciation analysis to find out correlations between mercury adsorption and concentration of dissolved species. To support this analysis, a comprehensive experimental study on mercury adsorption at different mercury concentrations, temperatures and pH was carried out in model aqueous solutions. This study pointed out that mercury capture occurs mainly through adsorption of cationic species, the adsorption of anions being significant only for basic pH. Furthermore, it was shown that HgOH + and Hg 2+ are captured to a higher extent than HgCl +, but their adsorption is more sensitive to solution pH. Tests on the effect of temperature in a range from 10 to 55 °C showed a peculiar non-monotonic trend for mercury solution containing chlorides. The chemical speciation and the assumption of adsorption exothermicity allow describing this experimental finding without considering the occurrence of different adsorption mechanisms at different temperature.