Hazard-free treatment of electrolytic manganese residue and recovery of manganese using low temperature roasting-water washing process.

• A process for hazard-free treatment electrolytic manganese residue (EMR) was proposed. • Almost all of the ammonia in the EMR was recovered by low-temperature roasting. • The manganese present in the EMR could be recovered by countercurrent water-washing. • The toxicity leaching results of the EMR after hazard-free treatment met GB 8978−1996. A combined low-temperature-roasting and water-washing process is investigated as a hazard-free method to treat electrolytic manganese residue (EMR) and recover manganese. In this study, the phase transformation characteristics and a thermodynamics analysis of the low temperature roasting process of EMR are evaluated. In addition, the effects of temperature and time on the phase transformation of EMR in the roasting process and the washing characteristics of roasted EMR samples are also investigated. Results reveal that some unstable phases within EMR are transformed into more stable phases depending on the treatment time/temperature conditions used and EMR roasted for 60 min at 600 °C (R 60min/600°C) exhibit the highest rate of manganese recovery, 67.12 %. After 25 min of deionized water washing, the concentration of manganese in solution from R 60min/600°C material become stable, whereas after 6 washing cycles the concentration of manganese in the solution is < 0.005 g/L. The R 60min/600°C material with three wash cycles results in a manganese-water solution concentration that is suitable for use in electrolytic manganese metal production. Finally, toxicity leaching tests show that the concentrations of ions present in the leaching solution are all lower than the regulatory limits mandated by the Chinese Integrated Wastewater Discharge Standard GB 8978−1996. [ABSTRACT FROM AUTHOR]