The dissolution of calcite in aqueous solution at pH < 4: kinetics and mechanism

摘要: The requirements of any experimental investigation a reaction, such as dissolution or precipitation, at the solid-liquid interface are delineated, and it is shown that no previously adopted method successfully meets all these criteria. A new strategy for studying reactions therefore proposed, described specifically kinetics calcium carbonate in acidic aqueous solution. This technique involves locating calcite crystal part one wall rectangular duct, through which reactant flows under laminar conditions, positioning either an amperometric potentiometric detector electrode immediately adjacent to downstream crystal. rate reaction surface then followed by measuring concentration products reaching function solution flow rate. In this way both transport (to detection system) topography defined controllable, and, most importantly, concentrations interrogated those pertaining not bulk values, probed with other (previous) methods. mechanistic model pH H + CaCO 3 → C 2 HCO − , developed, recognized half-, first- second-order constitute possible candidate heterogeneous processes. also takes following homogeneous (solution) into account: ⇌ O ⟶ k K = / backward implicit finite difference used provide theory proposed cell experiment. Specifically relates n th order process transport-limited current electrode, cell-crystal-electrode geometry. computational selected allows full parabolic velocity profile value be considered. validity numerical approach checked invoking Leveque approximation (linearizing profile) solving problem analytically 0 1. extended so parallel covered, describing can derived related design construction necessary apparatus described, along experiments devised prove approach. results carried out 0.25–1.0 mM HCl solutions presented, first time between transport-controlled. Assuming 20 s 1 3.06 × 4 M best fit data obtained first-order constant (0.043 ± 0.015) cm -1 .