Abstract
Several industrial activities produce metal sulfates, which are controlled by strict limitations for wastewater concentrations of sulfate. One emerging area where these activities occur is the production of lithium-ion battery chemicals in which sodium sulfates are formed because of cathode precursor co-precipitation. Several solutions for sulfate removal exist, but one option is to reuse the sulfate side stream in other processes to increase circular economy and atom efficiency. In this paper, the reuse of sodium sulfate solution in a steel industry pickling solution is considered. Neutral electrolytic pickling experiments were carried out to compare the pickling behavior of the electrolyte dissolved from pure sodium sulfate and the electrolyte diluted from a side stream solution. Effect of impure electrolyte was evaluated using field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectrometry (EDS). Concentrations of the metal ions were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). The results indicated a slight increase in current efficiency with the side stream electrolyte solution, while overall the pickling behavior remained similar. This suggests that a side stream sodium sulfate solution could be used as a pickling electrolyte, reducing the need for pure reagents.
Highlights
Both globally and in Finland, several industrial activities produce metal sulfates, which are controlled by strict limitations for wastewater concentrations of sulfate
The possibility of using sodium sulfate containing side stream elec trolyte (SE) solution from nickel hydroxide production was evaluated as an electrolyte solution in neutral electrolytic pickling of stainless steel
A comparison was made with reagent grade sodium sulfate solution (PE) of comparable conductivity
Summary
Both globally and in Finland, several industrial activities (e.g., metal refining, pulp production) produce metal sulfates, which are controlled by strict limitations for wastewater concentrations of sulfate. In Finland, the limits of the wastewater sulfate concentrations are determined by the environmental permission of the company. Sulfate ions are not considered hazardous, sulfate limitations are established to reduce the environmental strain caused by the increase in saline concentrations of natural waters, especially in fresh waters. The need to avoid salination while increasing industrial production requires more efficient methods for wastewater treatment, both for sulfate removal and for reusing sulfate-containing solutions. Sulfate recovery methods that reduce the sulfate concentration of purified wastewaters in a commercially viable and efficient way have recently become a point of interest of several studies (Dutrizac and Chen, 2005; Li et al, 2019; Rogener et al, 2012). A complementary possibility is to reuse a portion of the side stream sulfate solution in other processes, rather than as a waste, increasing circular economy and atom efficiency
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