Removal of arsenic and other amphoteric elements from solid wastes - by burning or decomposing contaminants, extracting with water and removing contaminants from water

摘要

Arsenic and/or amphoteric elements are removed from sludge or solid waste. The process comprises (a) subjecting to thermal treatment in the presence of air or oxygen or an alkaline reagent to burn organic components and decompose inorganic ones; (b) extracting with water; (c) treating the extract with an anion exchanger in OH form to bind the elements in anionic form; (d) eluting with an aq. alkaline liq. to regenerate the ion exchanger and form a soln. of the elements and (e) pptg. the elements in the form of an insoluble salt. Pref. the amphoteric elements are P, Cr, Al, Mn and/or Zn. The alkaline reagent is Na or K carbonate, hydrogen carbonate or hydroxide. The thermal treatment of Ag-contg. Fe hydroxide sludge is at 600-900 deg.C. The extracting water is demineralised. The anion exchanger is strongly basic. The eluant is NaOH or KOH. The precipitant is lime or milk of lime. If the starting material is free from organic matter, steps (a) and (b) are omitted and replaced by direct extraction with an aq. alkaline liq., esp. aq. NaOH or KOH.