Uptake of a Few Divalent Heavy-Metal Ion Species from Their Aqueous Solutions by Coral Sand Heat-Treated at Various Temperatures

Abstract

Mechanism and equilibrium relationships for the uptake of Cd²⁺, Cu²⁺ and Pb²⁺ by coral sand from their nitrate aqueous solutions were studied.
The maximum amounts of Pb²⁺ and Cd²⁺ uptaken by coral sand dried at 403 K were about 1.3 and 0.9 mol·kg^–1, respectively. That of Cu²⁺ was only about 1/100 that of Pb2²⁺ at pH = 6.1–5.5. Equilibrium relationships between the concentrations of those ionic species and the amounts uptaken were expressed by either the Langmuir or the Freundlich isotherm.
The amounts of those ions uptaken and the physical properties of the coral sand varied with the maximum temperature during treatment. For example, the B.E.T. specific surface area decreased with increasing heat-treatment temperature. This is due to the change in the crystallographic structure of calcium carbonate, which is the main component of the coral sand, from aragonite to calcite.