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Abstract
A certified clay mineral from Iraq, montmorillonite, is used for the adsorption of chromium and lead ions from water. Experimental design is utilized here to plan for the practical work and analysis of the results. Batch wise experiments are carried out to equilibrate Cr and Pb solutions (250 mg/L) individually and simultaneously with montmorillonite (5 - 20 g/L) at various pH ranges (2 - 7.5) for 10 - 60 minutes. The results indicate perfect fit with the model used. Chromium adsorption is sensitive to pH changes being high at neutral medium. Lead is almost independent of the pH of the solution. In nearly neutral medium, the sorption capacity of Cr is 21.4 and that of lead is 24.3 mg/g. The optimum conditions for >96% Cr removal are 12 - 15 g clay/L, 40 - 50 minutes and a pH of 5 - 7. For lead, almost 100% removal can be attained using 12 - 15 g clay/L, 40 - 50 min. at a pH of 4 - 6. The effects of various operating parameters are discussed. Simultaneously, the lead shows a greater tendency to sorption than chromium and a ratio of 5:4 can best represent the occupation of the active surface of the clay. The most favorable conditions for simultaneous removing of Cr, 86% and Pb, 100% may be 12.5 g/L clay content and a pH of 7.5 within 30 minutes. The kinetic study of the results indicates the adsorption follow pseudo-second order kinetics in which chemical interaction is also involved. The kinetic study confirms the dependence of chromium adsorption on the pH of the medium being favoured at high pH values.
Highlights
Chromium and lead are among the toxic heavy metals in the environment
The use of leaded gasoline declined in developed countries but was still used in other countries
Effective adsorption capacity of 21.46 mg/g for chromium was obtained within 40 - 50 in a neutral medium
Summary
Lead contamination comes mainly from lead in paint, gasoline, water distribution systems, food, and lead used in hobby activities. The use of leaded gasoline declined in developed countries but was still used in other countries. Water is contaminated in the distribution networks and the possibility of contamination will increase with the decrease of pH of water. When lead-paint is deteriorated, the risks of lead poisoning increase to children because of abrasion into dust. Food may be contaminated by the lead through the soil contaminated with lead or the use of insecticides that contain lead [1]. Lead in blood increases dramatically in the people who work in crowded intersections when leaded gasoline is still in use. Lead will move to living bodies by grazing and food chains. A recent study indicates that the wire and cable manufacturing and the rubber and plastic industry are the largest reported users of lead compounds [2]
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