ABSTRACT

The uptake of aqueous Ba²⁺ ions by abiogenic calcite and aragonite was studied over a wide range of concentration; 1.0 × 10¹, 5.0 × 10¹, 1.0 × 10², 5.0 × 10², 1.0 × 10³, 5.0 × 10³, and 1.0 × 10⁴ mg/L. The uptake process was characterized using ICP-AES, XRPD, SEM/EDS, and FTIR techniques. Up to the initial concentration of 5.0 × 10² mg/L, the uptake of Ba²⁺ ions was fast and obeyed Lagergren's kinetic model. The equilibrium data were adequately described using Freundlich isotherm model. The overgrowth of BaCO₃ (witherite) took place at higher concentrations, in a kinetically slow process and enhanced the uptake of Ba²⁺ ions. Quantitative XRPD was used to evaluate the fractions of precipitated BaCO₃ on calcite and aragonite minerals and monitor their variation with time. At all the studied concentrations, aragonite showed higher removal capacity of Ba²⁺ and faster uptake kinetics than did calcite. The precipitated crystals appeared to predominantly possess olivary-like morphology with an average particle size of 1-2 μm. EDS was used to reveal the elemental quantities of Ba and Ca after BaCO₃ formation on calcite and aragonite surfaces. FTIR spectroscopy was employed to analyze the vibrational modes in carbonate mixtures upon incorporation of Ba²⁺ by sorption and precipitation mechanisms.