Solidification and stabilisation of metal plating sludge with fly ash geopolymers

• Main Authors: Changjutturas, Kosawat, Hoy, Menglim, A. Rashid, Ahmad Safuan, Horpibulsuk, Suksun, Arulrajah, Arul
• Format: Article
• Published: ICE Publishing 2023
• Subjects: TA Engineering (General). Civil engineering (General)
• Online Access: http://eprints.utm.my/107267/; http://dx.doi.org/10.1680/jenge.19.00050
• Institution: Universiti Teknologi Malaysia

The disposal of metal plating sludge (PS) to landfills is an increasingly common practice in developed and developing countries. This paper presents a novel PS stabilisation technique using fly ash (FA)-based geopolymers as a waste management option. Strength and microstructural evaluations were carried out on PS-FA geopolymers at various values of factors, including liquid alkaline activator (L = sodium silicate (Na2SiO3)/sodium hydroxide (NaOH) ratio), L/FA ratios, FA/PS ratios and curing time. Increasing the amount of PS in PS-FA geopolymers reduced the total porosity, subsequently resulting in higher unconfined compressive strength (UCS) values. The main geopolymerisation product of the FA-based geopolymer was sodium aluminosilicate hydrate (N-A-S-H) gel. Since PS had a high calcium content, it would react with the high amount of silica and alumina present in FA to generate calcium aluminosilicate hydrate (C-A-S-H) gel in PS-FA geopolymers. This C-A-S-H gel coexisted with the N-A-S-H gel from FA-based geopolymers and hence significantly accelerated UCS development of PS-FA geopolymers over time. The UCS values of PS-FA geopolymers were found to meet the US Environmental Protection Agency requirement for disposal to landfills. The outcomes from this research can be translated into a regulatory framework for managing PS and diverting this industrial waste from landfills.