Recovery of soluble chlorides from municipal solid waste incineration fly ash using evaporative crystallisation and flotation methods

ABSTRACT

Fly ash contains large amounts of soluble chlorides, including KCl, NaCl, and CaCl₂. Currently, KCl and NaCl from the wastewater obtained after washing are separated mainly via evaporative crystallization, whereas CaCl₂ is preferentially precipitated using Na₂CO₃. These methods present poor separation performance of KCl and NaCl. In this study, evaporative crystallization was used to simultaneously separate KCl and NaCl mixture from CaCl₂. The solubility test results and theoretical recoveries of KCl and NaCl were used as a basis for the experiments. The recoveries of NaCl and KCl were 92.73% and 92.70%, respectively. Contact angle tests were performed to evaluate hydrophobicity of KCl and NaCl surfaces. The contact angle of a KCl–NaCl saturated solution containing flotation reagents on NaCl and KCl was 0° and 28.2°, respectively, indicating the complete hydrophilicity of NaCl and hydrophobicity of KCl. Separation of KCl and NaCl via flotation was analyzed and the effects of collectors, collector concentration, depressants, and pH on flotation efficiency were determined. Under optimal conditions, the grade and total recovery of KCl were 98.31% and 91.43%, respectively, whereas those of NaCl were 96.62% and 90.00%, respectively. Therefore, the combination of evaporative crystallization and flotation can be a promising method for separating soluble chlorides from fly ash.

KEYWORDS:

• Municipal solid waste incineration fly ash
• soluble chlorides
• evaporative crystallization
• contact angle
• flotation

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Science, Technology and Innovation Commission of Shenzhen Municipality [No. JCYJ20180503182130795] and the Technical Research Project of the Science and Technology Innovation Commission of Shenzhen [No. JSGG20190822102607176].