“…surface complexation, and non specific adsorption such as ion exchange [1]. The chemistry of Pb in soils is affected by three main factors: specific adsorption to various solid phases, precipitation of sparingly soluble or highly stable compounds and formation of relatively stable complexes or chelates with soil components [2][3] [4] [5] investigated the retention of Pb 2+ ion by montmorillonites and found that cation exchange predominated in pH range 2 -4, precipitation was the main mechanism at pH > 6, and a combination of both took place at intermediate pH 4 -6. A strong dependence on ionic strength is typical for an outer-sphere complex, whereas insensibility of ionic strength is an indication for inner sphere surface complexation [6].…”