Reduction of steel slag leachate pH via humidification using water and aqueous reagents

Bo Chen; Sangwon Yoon; Yi Zhang; Longxi Han; Yongju Choi

doi:10.1016/j.scitotenv.2019.03.362

Reduction of steel slag leachate pH via humidification using water and aqueous reagents

Sci Total Environ. 2019 Jun 25:671:598-607. doi: 10.1016/j.scitotenv.2019.03.362. Epub 2019 Mar 25.

Authors

Bo Chen¹, Sangwon Yoon², Yi Zhang³, Longxi Han³, Yongju Choi⁴

Affiliations

¹ Key Laboratory of Integrated Regulation and Resource Development on Shallow Lake of Ministry of Education, College of Environment, Hohai University, Nanjing, China; Department of Civil and Environmental Engineering, Seoul National University, Seoul, Republic of Korea.
² Department of Civil and Environmental Engineering, Seoul National University, Seoul, Republic of Korea.
³ Key Laboratory of Integrated Regulation and Resource Development on Shallow Lake of Ministry of Education, College of Environment, Hohai University, Nanjing, China.
⁴ Department of Civil and Environmental Engineering, Seoul National University, Seoul, Republic of Korea; Institute of Construction and Environmental Engineering, Seoul National University, Seoul, Republic of Korea. Electronic address: ychoi81@snu.ac.kr.

PMID: 30933816
DOI: 10.1016/j.scitotenv.2019.03.362

Abstract

A slag humidification process that aims to reduce the leachate pH of steel slag via carbonation was accomplished by simply wetting the slag and exposing it to the atmosphere for passive diffusion of atmospheric CO₂. The optimization parameters of the process were studied. Results showed that by wetting the slag using various aqueous solutions (deionized water, NaCl solution and NaOH solution), such that its moisture content nearly reaches its water holding capacity, a significant reduction in leachate pH could be achieved. Pretreatment of the slag using 1 M NaOH and subsequent humidification using deionized water showed the best efficiency of 1.1 pH unit reduction among the tested conditions. Slag pretreatment could substantially enhance the carbonation degree on the slag surface, leading to conservation of the treatment effectiveness up to three times the leachate replenishment using deionized water. The benefit of the alkaline treatment to promote slag carbonation could also be achieved using a low to moderate (0.005-0.1 M) NaOH solutions for humidification without the pretreatment step. A 72.5% increase in the treatment efficiency could be achieved via a humidification treatment using 0.005 M NaOH solution compared to that using deionized water. This study shows the promise of humidification treatment as a low-cost, easily implemented, and environmentally friendly slag pH neutralization process that can be applied in the field for slag treatment prior to its use or disposal in the environment.

Keywords: Accelerated carbonation; Alkaline pretreatment; Humidification; Leachate pH reduction; Salinity.