Process integration and techno-economic assessment of crystallization techniques for Na2SO4 and NaCl recovery from saline effluents

Abstract

Saline effluents containing primarily sodium chloride (NaCl) and sodium sulfate (Na2SO4) are generated from common salt production, tannery CETPs, textiles industries, desalination rejects, etc. In this work, experimental studies have been conducted for parametric evaluation of crystallization techniques for selective isolation of Na2SO4 and NaCl from saline effluent. Three crystallization approaches, i.e., evaporation-crystallization, cooling-crystallization, and antisolvent-crystallization, are assessed through parametric studies. A representative saline solution generated from a salt refinery unit is considered for the study. Lab-scale experiments were performed to determine the optimum process conditions for each crystallization process, and their performance was evaluated by estimating the separation efficiency. Chemical, P-XRD, and TGA analyses were performed to characterize the product composition, purity, and hydration state. For selective Na2SO4 recovery, cooling crystallization, and antisolvent crystallization were found suitable over evaporation crystallization. Subsequently, integrated process variants for cooling crystallization and antisolvent crystallization-based separation were developed. A techno-economic assessment (TEA) was performed to compare integrated process variants for the recovery of salts (Na2SO4 and NaCl) and establish the prospective towards commercialization. The parametric evaluation and TEA shows that the combined crystallization technologies can be potential approach to recover added-value products from saline effluents promoting waste to wealth notion.