Effects of natural acids on surface properties of asbestos minerals and kaolinite

Serpentine, and other asbestos minerals, are considered potential hazards to human respiratory health. It has been postulated that the surface characteristics of these substances, such as surface charge and adsorbed metals, notably Fe and other transition metals, may be the major agents responsible for their toxicity. There is a general consensus that the amphibole group of minerals possesses a greater health risk than serpentines dominated by chrysotile. There have been suggestions that natural processes can alter the surfaces of these minerals and reduce their potency. This study examined the effects of carbonic acid, oxalic acid and hydrochloric acid on the surface characteristics of two trioctahedral minerals, actinolite (amphibole) and chrysotile (serpentine), and compared the results to a non-asbestiform, dioctahedral mineral, kaolinite. Results confirm that the treatments alter the mineral surfaces by changing the zeta potential of the asbestiform minerals from positive to negative and by removing considerable amounts on non-crystalline Fe and other metals. X-ray analyses indicated that mineral structure was little affected by the treatments, and TOF-SIMS revealed that treatments did remove surface adsorbed metals and cations in octahedral coordination within the samples.