Eco-friendly and sustainable process for recovery of sulfate from paper mill mixed salt: Recycling of sulfate for dye fixation process

Paper mill Electrostatic Precipitator (ESP) ash contains a mixture of alkali metal chloride (34.2 %) and sulfate (84.2 %) which has serious negative effects on the environment and makes it more expensive and constrained to dispose ESP ash. Therefore, handling and recycling ESP ash demands extra thought when disposing of it. Present study, aimed to separate chloride and sulfate from ESP ash using electrochemical membrane technology. Three different concentrations of ESP ash solution such as 200 g L-1, 320 g L-1 and 450 g L-1 were used as the electrolyte. Ti/TiO2–IrO2–RuO2 and titanium (Ti) are used as anode and cathode respectively. Caustic and sulfate solutions were recovered at the respective compartments. The collected sulfate solution was dried by solar light to convert 99 % sulfate salts as confirmed by Energy-dispersive X-ray analysis (EDAX) analysis. Recovered sulfate salt was used for the dye fixing process, in which the colour fixing difference of ΔE value was about 2.10 and the strength of the dye was about 86.72 %. Therefore, the textile industry can repurpose the recovered sulfate salt for the dye fixing process. [Display omitted] •An electrochemical membrane process was adopted to treat the ESP ash slat.•Na2SO4, Cl2 and alkali were recovered in a single electrochemical process.•Double layer cation exchange membrane provided good current efficiency.•Recovered Na2SO4 was used in the dyeing process and ΔE is 2.10 and dye strength is 86.72 %.•Sulfate concentration does not affect the CEM in the electrochemical process.