Monitoring the removal of carbonate from alkali metal hydroxide solutions using gas diffusion flow injection

Abstract

Monitoring the removal of carbonate from alkali metal hydroxide (MOH, M = K, Na) solutions with calcium oxide (CaO) was studied using a newly developed method for the determination of trace amounts of total carbonate (TC) in alkaline solutions based on a flow injection (FI) technique coupled with a gas diffusion system. The optimized conditions of the FI system were as follows: the flow rate of each carrier, reaction solution (H₂SO₄) and receptor solution (Cresol Red, pH 8.9) was 0.25 ml min⁻¹, the sample size was 0.1 ml and the concentration of H₂SO₄ in the reaction solution was 0.09 M. The limit of detection of TC by the proposed method was 4 × 10⁻⁷ M. The removal efficiency of carbonate was affected by the amount of CaO added, the shaking time of the solutions and the concentration of MOH. For 1 M NaOH and KOH solution, the removal efficiency of carbonate was about 99% and the concentration of residual carbonate was 4 × 10⁻⁵ and 1.2 × 10⁻⁴ M, respectively, when the amount of CaO added was 2 g l⁻¹ and the shaking time was 16 h.