Stabilization/solidification of chromium-bearing electroplating sludge with alkali-activated slag binders. (February 2020)

• Record Type: Journal Article
• Authors: Chen, Huxing; Yuan, Honghong; Mao, Linqing; Hashmi, Muhammad Zaffar; Xu, Fangnan; Tang, Xianjin
• Is Part Of: Chemosphere. Volume 240(2020)
• Publication Date: 2020-02
• Subjects: Alkali-activated -- Blast furnace slag -- Chromium -- Electroplating sludge -- Stabilization -- Solidification; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2019.124885
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: Chromium (Cr)-bearing electroplating sludge is a hazardous solid waste and has a detrimental effect on human health and the environment. In this study, an alkali-activated slag binders, namely, formed by the reaction of blast furnace slag (BFS) with alkali, was applied to the stabilization/solidification (S/S) of electroplating sludge. The effects of liquid–solid ratio, water glass modulus ratio (molar ratio of SiO2 to Na2 O), water glass dosage, and electroplating sludge amount on the compressive strength and Cr leachability of binders were analyzed. The related mechanism of the S/S of electroplating sludge was discussed on the basis of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy coupled with energy-dispersive spectrometry (SEM–EDS). Results showed that the compressive strength of the alkali-activated slag binder first increased and then remained stable with the increase in liquid–solid ratio, water glass modulus ratio, and water glass dosage. By contrast, the leaching concentrations of Cr(VI) and total Cr decreased with the increase in liquid-solid ratio, water glass modulus ratio, water glass dosage, and curing time. In addition, XRD, FTIR, and SEM–EDS revealed that the hydration products of the binders were mainly low-crystallinity and dense calcium silicate hydrate gels, and Cr(VI) had been effectively immobilized in the structure. The reduction in Cr(VI) by the reductive components in the BFS boosted the stabilization of Cr-bearing electroplating sludge. Overall, the BFS binders containing electroplating sludge had relatively high compressive strengths and low Cr(VI) leaching concentrations. The physical encapsulation, chemical bonding, and absorption contributed the Cr immobilization during the S/S process of electroplating sludge. Highlights: The alkali-activated binders can be used as a building material. Cr can be effectively immobilized in the alkali-activated BFS binders. The alkali-activated binders can convert Cr(VI) to Cr(III) without any additional reductants. The alkali-activated BFS binders are mainly amorphous dense calcium silicate hydrate gels.