Arsenate incroporation in gypsum probed by neutron, X-ray scattring and density functional theory modeling

Crystallography is used for studying the synthetic gypsum coprecipitated with arsenic at different concentrations and pH values and neutron and X-ray diffraction are used for analyzing the solid phases. The charge redistribution within the structure ion substitutions of either the protonated or the unprotonated arsenate species has shown an increase in the covalency in the interaction between [Ca.sup.2+] and As[O.sub.4.sup.3-], whereas the interaction between [Ca.sup.2+] and HAs[O.sub.4.sup.2-] has remained predominantly ionic.