Optimization of Removal of Calcium Ions Forming During Synthesis of Boric Acid from Ulexite Ore by Using Ion Exchange Resin

Abstract

Ulexite (Na2O·2CaO·5B2O3·16H2O) is one of the most important raw materials for boric acid, synthesized by dissolving the ore in an acid solution. Since ulexite ore was dissolved in a phosphoric acid solution, the final solution included boric acid (H3BO3), sodium dihydrogen phosphate [NaH2PO4], and calcium dihydrogen phosphate [Ca(H2PO4)2]. The presence of several ions in the solution causes separation problems for boric acid. This study includes a special separation step to increase the purity of the boric acid that is synthesized from the dissolution of ulexite ore in phosphoric acid. For this purpose, calcium ions in the final solution were removed using Dowex HCR-S cationic ion exchange resin. Additionally, the Taguchi optimization method was employed to monitor the removal of calcium ions. The design of experiments included an orthogonal array technique in L9 array for three parameters with three different values; reaction temperature (12 oC, 25 oC, 40 oC), stirring rate (250 rpm, 300 rpm, 350 rpm), and the amount of resin material (10% wt., 30% wt., 50% wt.). The results of the calculations revealed that the optimum values of temperature, stirring rate, and amount of resin are 12 oC, 350 rpm, and 50% wt., respectively. The amount of calcium removed under optimum conditions was found as 79.49%.