Separation of arsenic from hazardous As-bearing acidic leached zinc plant purification filter cake selectively by caustic baking and water leaching

- Thermodynamic behaviors of metals including in ALZPHPFC were evaluated.
- Caustic baking and subsequently water leaching process was applied successfully.
- As was extracted completely and also high selectively over impurities mainly Zn and Pb.

In the present study, a process for complete and selective separation of arsenic from As-bearing acidic leached zinc plant hot purification filter cake (ALZPHPFC) over impurities mainly zinc and lead was examined so that by decreasing the weight percentage of arsenic in ALZPHPFC environmental problems would be eliminated and dumped safely. In this line, using either NaOH or NaOH-H2O2, ALZPHPFC was first treated through direct alkaline leaching (DAL) process. DAL process failed to leach satisfactory amount of arsenic from ALZPHPFC, and also selective arsenic extraction over zinc and lead through DAL process was not feasible. Therefore, caustic baking and subsequently water leaching process was applied to examine the possibility of satisfactory and selective arsenic extraction. Investigation of the effect of all parameters showed that only NaOH/ALZPHPFC wt. ratio and baking temperature and time made significant changes on metal extraction, and by increasing the mentioned parameters, arsenic extraction via caustic baking process improved. So hydroxide anions in media, and consequently zinc and lead extraction decreased in higher baking temperature and time. But at higher NaOH/ALZPHPFC wt. ratio zinc and lead extraction increased because of higher filtrate pH. The results have indicated that almost all of arsenic could be extracted selectively from ALZPHPFC when it was baked for 4 h at 600 °C with a NaOH/ALZPHPFC wt. ratio of 1.