The influence of ph and adsorbent concentration on adsorption of lead and zinc on a natural goethite

Adsorption characteristics of Pb and Cd were conducted on a natural goethite from Kaduna (Niperia) and compared same with a synthetic goethite. The adsorption data was fitted into Langmuir model which gave Langmuir constants k and Xm for Pb and Cd as 4.99 & 2.40 and 1.43 & 1.05 respectively. The adsorption behavior was essentially the same, although, synthetic goethite sorbed a little more metal ion than the natural goethite. This was attributed to the higher proportion of goethite in synthetic than natural goethite per unit mass of sample rather than greater chemical reactivity of the synthetic goethite. The influence of variable pH and adsorbent concentrations on the sorption of Pb and Cd by the natural goethite was studied. Sorption efficiency was greatly governed by pH with nearly 100% adsorption of Pb occurring at initial pH of 5. Generally, Pb was sorbed more strongly with increasing pH from 3 to 5 than Cd and thus poses less environmental threat. Efficient removal of Pb was achieved at lower dose of goethite, as there was no appreciable increase in the amount of Pb adsorbed when the adsorbent dose was increased.