The Mechanism of Calcite Dissolution Using Environmentally Benign Polyaspartic Acid

摘要

Polyaspartic acid (PASP), an environmentally benign sequestrant, is investigated as a cleaning agent for the removal of calcium minerals from solid surfaces. The focus of this study is to elucidate the chemical and interfacial mechanisms of calcite (calcium carbonate) dissolution in PASP solutions by the use of the rotating disk technique. Controlled mass transfer rotating disk studies indicated an increase in the rate of calcite dissolution with increasing PASP concentration and decreasing pH. Calcite dissolution occurs primarily via an interfacial reaction limited process in alkaline pH regime, and a mass transfer limited process at low PASP concentrations in acidic pHs. Furthermore, increasing polymer concentration under acidic pH conditions or increasing pH raises the contribution of the interfacial controlled dissolution mechanism. SEM evaluation of the surface indicates significant variations in the interactions of the polymer with the calcite surface during dissolution at different conditions. Experimental results also revealed that calcite dissolution in acidic pH regime is dependent on the molecular weight of the polymer. A kinetic model incorporating interfacial interaction, chelation chemistry and mass transfer has been developed to interpret the experimental phenomena.