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 forboric acid, synthesized by dissolving the ore in an acid solution. Since ulexiteore was dissolved in a phosphoric acid solution, the final solution included boricacid (H3BO3), sodium dihydrogen phosphate [NaH2PO4], and calcium dihydrogenphosphate [Ca(H2PO4)2]. The presence of several ions in the solution causesseparation problems for boric acid. This study includes a special separation stepto increase the purity of the boric acid that is synthesized from the dissolution ofulexite ore in phosphoric acid. For this purpose, calcium ions in the final solutionwere removed using Dowex HCR-S cationic ion exchange resin. Additionally, theTaguchi optimization method was employed to monitor the removal of calciumions. The design of experiments included an orthogonal array technique in L9 arrayfor three parameters with three different values; reaction temperature (12 oC, 25oC, 40 oC), stirring rate (250 rpm, 300 rpm, 350 rpm), and the amount of resin(10% wt., 30% wt., 50% wt.). The results of the calculations revealed that theoptimum values of temperature, stirring rate, and amount of resin are 12 oC, 350rpm, and 50% wt., respectively. The amount of calcium removed under optimumconditions was found as 79.49%.