Borax preparation from Na-B-Si-containing solution by carbonation and multi-step crystallization

Abstract

The Na-B-Si-containing solution was derived from ludwigite ore through a two-step process involving soda-ash roasting and subsequent grind-leaching. This study employed a carbonation-crystallization approach to comprehensively utilize the valuable components in the solution, aiming to produce borax while simultaneously generating sodium carbonate and silica. The initial carbonation precipitation achieved a high desilication ratio of 95.54 % through nano-sized silica particle formation. Meanwhile, the boron conversion ratio reached 94 %, with negligible boron loss due to efficient metaborate-to-borate transformation. To guide the crystallization separation of Na2CO3 and Na2B4O7, phase diagrams of the ternary system (Na2CO3 + Na2B4O7 + H2O) were experimentally constructed at 308.15 k and 333.15 k. Crystallization was then conducted at 278.15 K for 2 h, yielding a Na2B4O7·10H2O product with 96.45 % purity. The remaining filtrate was evaporated and crystallized to obtain the Na2CO3 product, which can be reused in the previous roasting process.