Sodium-sulphate production from sulphate-rich bittern: A parametric study and economic evaluation

Abstract

Concentrated brines and bitterns rejected from various processes contain mineral salts of economic value. For example, sulphate-rich bittern generated at saltworks in the Rajasthan state of India exceeds 3 million tons annually and requires adequate treatment. Resource recovery from such unutilized by-products presents a sustainable waste management approach. This work presents the development and evaluation of a process for sodium-sulphate (Na2SO4) recovery from sulphate-rich bitterns using an integrated process combining cooling crystallization, filtration, and drying as major unit operations. A parametric study has been conducted to investigate the effect of various operating parameters on product (anhydrous sodium-sulphate) yield and quality. Chemical analysis, TGA, P-XRD, and SEM-EDX techniques were used to characterize the product quality and purity. Based on the parametric studies, a sodium-sulphate production process was designed, and material & energy balance was established. The mass balance calculations have shown that 1 ton of anhydrous Na2SO4 (~97 wt% purity) can be produced from 6.31 tons of bittern having a sulphate ion concentration of about 140.8 ± 6.94 g/l. Subsequently, the economic feasibility of a 5 ton/day anhydrous Na2SO4 capacity plant has been evaluated using the cost and profitability analysis. The engineering-economic calculations suggest that the sodium-sulphate production from bittern can be economically favourable, achieving a payback period of 3.5 years. The optimized parameters and economics presented in this paper could significantly help implement an actual sodium-sulphate recovery unit using sulphate-rich bittern as feed.