The volcanic soil of Southern Chile was tested for its heavy metal retention capacity. The maximum uptakes for CrO₄ ^2- (CrVI), Cu²⁺, Zn²⁺ and Pb²⁺ were determined to be 2.74, 5.32, 5.86 and 7.44 mg g^-1, respectively. At a slightly alkaline pH value (7.5), it seems that a precipitation-adsorption process was responsible for the Cu²+ and Zn²+ uptake onto volcanic soil. All the determined values are of the same order of magnitude as natural zeolites heavy metals adsorption capacities. In addition, the heavy metals diffusion model through a 1 m volcanic soil mineral liner shows breakthrough times of 21.6, 10.2 and 8.9 years, for Pb²⁺, Zn²⁺ and Cu²⁺, respectively, confirming the trend obtained in the adsorption isotherms. The natural volcanic soil of Southern Chile is an interesting material for possible use as landfill mineral basal sealing. It has an appropriate sealing potential (average K _f value of 5.85 × 10^-9 m s^-1) and a heavy metals retention capacity comparable with natural zeolites. About two-thirds of the agricultural land in Chile (approximately 0.4 million km²) is derived from volcanic ash, suggesting an important soil volume for future landfill projects, that could be obtained in sufficient quantities from urban building activities.

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The use of volcanic soil as mineral landfill liner - III. Heavy metals retention capacity