Understanding and controlling the key crystal phase transformation for recovery of sodium chloride from organic waste salt

Abstract

The salt waste accompanied with organic pollutants is a kind of toxic solid waste during the chemical production process. To date, there are still lack of satisfactory treatments for it. This work proposed a simple method for dispose the methanol conaminated salt waste through roasting at moderate temparture. The composition analysis by the X-ray powder diffraction, the fourier transform infrared spectroscopy and the scanning electron microscope-mapping shows the crucial phase of organic components that adhere to the surface of NaCl crystal are mostly in the phase of calcium methoxide (Ca(OCH3)2), which leads to the agglomeration of sodium chloride and is not suitable for conventional treatment methods. It is found that the surface Ca(OCH3)2 could be transformed into calcium carbonate (CaCO3) by roasting at low temperature of ∼ 270 °C, resulting in the removal of the organic matter in the waste. Then it was further roasted at 600 °C for the decomposition of surface CaCO3 which may prevent the dissolution and the subsequent recovery of NaCl. The results illustrated that NaCl can be effectively recovered with a high purity of 98.80 %. Furthermore, the TOC value of its saturated solution decreased from 7.07 × 104 to 40.14 mg/L, far below the limits (200 mg/L) in chlorine alkali plant. This work proposes a promising treatment method to recover salt resources from waste salt, and provides new insights into the function of controlling the key phase.