Production of crystalline boric acid and sodium citrate from borax decahydrate

• Crystalline boric acid was produced from borax.
• Trisodium citrate dihydrate was obtained from the mother liquor.
• Borate mineral - organic acid reactions are extensively summarized.
• The overall reaction can be written as follows:3 Na2B4O7·10H2O(s) + 2 C6H8O7·H2O(s) + 4 H2O(l) → 12 H3BO3(s) + 2 Na3C6H5O7·2H2O(s) + 17 H2O(l)

Tincal, colemanite and ulexite are the most commercially significant borate minerals. The commercial production of boric acid from these minerals is based on a mineral–inorganic acid reaction. In this study, crystalline boric acid (H3BO3) was produced from borax decahydrate using an organic acid, and trisodium citrate dihydrate (Na3C6H5O7·2H2O) was also obtained via crystallization from the residual mother liquor. The products were identified by X-ray powder diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric and differential thermal analysis (TG-DTA). The impurities in the boric acid products were determined by inductively coupled plasma spectroscopy (ICP-OES), ion chromatography, and total organic carbon (TOC) analysis. Boric acid was separated from reaction mixture via batch crystallization and the recovery yield was achieved 69%. The purity value of the crystals was increased from 97.5% to 99.9% by recrystallization. The proposed production method may be more attractive than the current commercial processes because it deals with green and sustainable process, preventing a high consumption of inorganic acids and generation of solid waste. Moreover, the trisodium citrate obtained as a by-product is a high value-added chemical.