Abstract
Demand for nickel and cobalt sulfate is expected to increase due to the rapidly growing Li-battery industry needed for the electrification of automobiles. This has led to an increase in the production of sodium sulfate as a waste effluent that needs to be processed to meet discharge guidelines. Using bipolar membrane electrodialysis (BPED), acids and bases can be effectively produced from corresponding salts found in these waste effluents. However, the efficiency and environmental sustainability of the overall BPED process depends upon several factors, including the properties of the ion exchange membranes employed, effluent type, and temperature which affects the viscosity and conductivity of feed effluent, and the overpotentials. This work focuses on the recycling of Na2SO4 rich waste effluent, through a feed and bleed BPED process. A high ion-exchange capacity and ionic conductivity with excellent stability up to 41 °C is observed during the proposed BPED process, with this temperature increase also leading to improved current efficiency. Five and ten repeating units were tested to determine the effect on BPED stack performance, as well as the effect of temperature and current density on the stack voltage and current efficiency. Furthermore, the concentration and maximum purity (>96.5%) of the products were determined. Using the experimental data, both the capital expense (CAPEX) and operating expense (OPEX) for a theoretical plant capacity of 100 m3 h−1 of Na2SO4 at 110 g L−1 was calculated, yielding CAPEX values of 20 M EUR, and OPEX at 14.2 M EUR/year with a payback time of 11 years, however, the payback time is sensitive to chemical and electricity prices.
Highlights
The mining and metallurgical industries produce large amounts of waste during the processing and neutralization of acidic streams [1]
We have shown that the bipolar membrane electrodialysis (BPED) process can be used to effectively treat waste sodium sulfate effluent streams
It was observed that the temperature increase led to an improvment in current efficiency
Summary
The mining and metallurgical industries produce large amounts of waste during the processing and neutralization of acidic streams [1]. Cation exchange membrane (CEM) current efficiency is drastically dropped from 100% to 83% due to an increase in proton leakage They achieved purity values of 99% for NaOH and 90% for H2SO4. With newer homogeneous membranes such as those offered by SUEZ Water Technologies and Solutions [34], higher purity products can be produced at elevated temperatures and at higher current density We tested these membranes in order to determine the commercial viability of the process. The aim of the study is to check the performance of the SUEZ membranes in a BPED stack with 5 and 10 repeating units of a BCA (BPM-CEM-AEM) configuration at different temperatures and current densities. This cost off-set leads to an estimated payback time of 11 years
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