A novel use for oil-contaminated drill cuttings in the manufacture of lightweight aggregate

Contaminated waste drill cuttings produced from drilling activities in the North Sea is currently transported onshore and landfilled at high costs, as there is no existing option for alternative and viable recycling. The aim of this research was therefore to investigate the technical feasibility of transforming this waste into an inert, porous, ceramic material to potentially be utilised as lightweight aggregate (LWA). In this project, three samples of waste drill cuttings were obtained and characterised for chemical compositions, mineralogy, thermal behaviour and contaminant leaching. To manufacture LWA, the raw materials were dried, ball milled, formed into pellets and fired above their initial sintering temperature. The effect of firing temperature on particle density, water absorption, compressive strength and microstructure was studied and compared with those of standard commercial products such as LECA and Lytag. The mineralogy before and after firing and its effect on leaching behaviour was also investigated. Washing pre-treatments were employed to mitigate the leaching of chlorides in the manufactured LWA and the potential of milled waste glass incorporated into LWA as a matrix forming material was evaluated. Finally, the research proposed a novel approach for calculating carbon dioxide emissions for the production of drill cuttings LWA.The results of this research showed that drill cuttings contained variable amounts of minerals with poor sintering capabilities. This limited their viability to be readily used as a raw material in LWA production – due to the unfavourable physical properties and environmental compatibility of the final products. In samples with high concentrations of chloride salts, a two-step washing pre-treatment using deionised water at an L/S ratio of 10 l/kg was necessary for leaching to comply with the End of Waste criteria. In samples with high concentrations of barium sulphate and carbonate minerals, the addition of 40 wt.% waste glass in the mix and firing at 1150 °C, produced LWA with physical properties comparable to commercially available products. However, mitigating the leaching of sulphates remained a challenge in samples with high initial concentrations of drilling fluids. Carbon dioxide emissions as low as 236.0 kg per 1.0 tonne of drill cuttings LWA were estimated and compared favourably with those for current management scenarios and other waste derived LWA. Overall, the research showed that LWA manufacturing represents a beneficial reuse of drill cuttings that diverts waste from landfill.