Reuse of spent bleaching earth by polymerisation of residual organics

• Spent bleaching earth contains a residual organic fraction that can be polymerised.
• The characteristics of spent bleaching earth catalyse polymerisation reactions.
• Optimum treatment involves low pressure compaction and heat treatment at 150 °C.
• This produces monolithic blocks with high compressive strength.
• The process developed allows novel reuse of a problematic waste.

Spent bleaching earth (SBE) is a waste generated by the edible oil industry that currently has limited options for beneficial reuse. In excess of ∼2 million tonnes per year of SBE is generated world-wide with major quantities available in the middle-east where significant volumes of edible oils are produced. Low pressure compaction followed by heat treatment at 150 °C causes polymerisation of the residual organic components in SBE and this produces monolithic samples with high unconfined compressive strengths (54 MPa). SBE can therefore be used to manufacture novel clay blocks for use in construction that are bonded by polymerised vegetable oil. This represents a new, innovative and resource efficient application for SBE. In this research, commercial SBE has been characterised and the effects of key processing variables (temperature and compaction pressure) on the compressive strength, porosity and density of the SBE clay blocks are reported and the mechanisms responsible for strength development are discussed.