Enhanced dewatering and stabilization of landfilled tannery sludge using combined draining and chemical-conditioning method: Performance evaluation and mechanisms

Xu, Yang, Gan, Quan, Jin, Fei ORCID: https://orcid.org/0000-0003-0899-7063, Liu, Xiaowen, Yu, Ran, Wang, Xin, Wan, Jihong and Du, Yan-Jun 2026. Enhanced dewatering and stabilization of landfilled tannery sludge using combined draining and chemical-conditioning method: Performance evaluation and mechanisms. Journal of Rock Mechanics and Geotechnical Engineering 10.1016/j.jrmge.2026.06.016

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Abstract

Tannery sludge contains high water content, substantial organic matter, and elevated heavy metals, yet over 90% has historically been landfilled in China without proper pre-treatment, posing significant environmental risks. This study proposes a novel in-situ treatment method that simultaneously dewaters and stabilizes landfilled tannery sludge by coupling draining (vacuum preloading with PVDs) and chemical conditioning with polymeric ferric sulfate (PFS) and calcium carbide residue (CCR). Macroscopic tests including vacuum filtration, batch leaching, and vacuum preloading model tests were conducted to optimize the dosages of PFS and CCR, and evaluate the effectiveness in dewatering and heavy metal stabilization. Microscopic tests including MIP, SEM, and heavy metal speciation analysis were performed to elucidate the mechanisms underlying the improvements in physical, chemical, and mechanical properties of the treated sludge. Vacuum filtration and batch leaching test results showed the optimal dosages of PFS and CCR were 12.5% and 8% (dry basis), respectively. Compared to unconditioned draining, the combined method yielded superior performance: lower water content (73% vs. 58.1%), greater volume reduction (7% vs. 48.7%), and significantly improved unconfined compressive strength (6 kPa vs. 70 kPa). The sludge closer to the PVD showed reduced water content and leachability, and increased strength, heavy metal content, and colloidal fraction when treated with the combined method. These phenomena were attributed to the synergistic effects of pore water drainage, colloid migration, and heavy metal immobilization. The findings support the application of the combined method for the effective in-situ treatment of landfilled tannery sludge.

Item Type:	Article
Date Type:	Published Online
Status:	In Press
Schools:	Schools > Engineering
Publisher:	Elsevier
ISSN:	1674-7755
Date of First Compliant Deposit:	11 August 2026
Date of Acceptance:	3 June 2026
Last Modified:	11 Aug 2026 11:15
URI:	https://orca.cardiff.ac.uk/id/eprint/188888

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