Recovery of Calcium from Reaction Fly Ash

Abstract

Reaction fly ash contains a large number of harmful substances, so it is usually solidified and buried in landfills. To improve the problem of insufficient landfill space, this study recovers CaOH from reaction fly ash to achieve mass and volume reduction. The leachate obtained by leaching the reaction fly ash with de-ionized water and 2N hydrochloric acid was used in the experiments, respectively. The volume reduction with 2N hydrochloric acid had better performance than de-ionized water, representing more than 90%. The leaching efficiency of Ca reached 21.06% with de-ionized water for 20 min at a condition of 25 °C and 7 mL/g pump density. The chemical precipitation with NaOH was conducted immediately after the completion of the leaching experiment, with a precipitation efficiency of CaOH reaching 98.55%. The leaching efficiency of Ca reached 70.26% with 2N hydrochloric acid for 30 min at a condition of 25 °C and 10 mL/g pump density. The chemical precipitation with NaOH and ion exchange with IRC748 were conducted, respectively, after the completion of the leaching experiment. After two precipitations, the precipitation efficiency of CaOH was 99.93%. The precipitation efficiency and purity of Ca after ion exchange separation were 99.90% and 98.91%, respectively. This work provided an effective approach to recover CaOH from reaction fly ash and accomplished volume reduction at the same time.