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

Production of Clay Coated Lightweight Fill Materials From Air Pollution Control Residues (APCR)

Air pollution control residues (APCr) from energy-from-waste are classified as hazardous due to their high heavy metal content and alkalinity. Recycling attempts using thermal treatment to produce a ceramic material known as lightweight aggregate have been successful in incorporating a maximum of 10% of APCr in the final product’s structure. The aim of this work was to increase this incorporation by producing macro-encapsulated APCr granules with a clay coating. APCr has been washed with deionized water, milled and mixed with different concentrations of sodium silicate to form into granules. Sodium silicate solution was added to the mix to enhance the content of silicate and flux. The green pellets were coated with clay and sintered in a laboratory furnace at 1150 °C. The effect of addition of sodium silicate on particle density, water absorption and compressive strength has been discussed. Leaching behaviour of heavy metals and soluble anions from the sintered granule was examined according to BS EN 12457. Optical micrographs of the sintered products were investigated to reveal the microstructure of the binding interface between APCr and clay coating. The results showed that incorporation of up to 30% of APCr in the structure of sintered granules is possible. The proposed clay coating technique is simple and can reduce the leaching behaviour of hazardous waste

Use of clay in the manufacture of lightweight aggregate

Clay is used as a raw material for the production of lightweight aggregates because it is readily processed into suitable granules and forms low-density but high strength aggregate particles when sintered at relatively low temperatures. The use of waste clay generated by major infrastructure development projects to make lightweight aggregate has a positive environmental impact and contributes towards a more circular economy. This paper reviews the manufacturing process used to produce lightweight aggregates from clay and the influence of processing conditions on properties. It also reviews secondary materials that have been incorporated into clays to produce lightweight aggregates. Additional research is required to improve understanding of the effects of composition and production parameters on the pore structure, density, water adsorption and strength of clay derived lightweight aggregates

Bauxite residue (Red mud) as a pulverised fuel ash substitute in the manufacture of lightweight aggregate

This study looked at the potential of bauxite residue or red mud to be used in the manufacture of lightweight aggregate in replacement of pulverised fuel ash (PFA), commonly used as a way of recycling problematic wastes. The percentage replacements of red mud with PFA were as follows: 25, 31, 38, 44 and 50%. These were blended in a mix with waste excavated clay and sewage sludge – all from the Chongqing municipality in China. Lightweight pellets were produced using a Trefoil rotary kiln and were sintered to 1200 °C. Results showed that 44 % bauxite residue replacement produced lightweight pellets with the highest compressive strength, highest density and largest water holding capacity. This would be expected in materials with a low level of silicates, which causes insufficient glass phase viscosity and therefore poor bloating during firing; producing an aggregate with a higher density but with open pores that allowed for larger water absorption. All ratios of red mud aggregates were significantly reduced in pH after firing to around pH 8, and this reduced the leachability of the aggregates to levels below those set by the European landfill directive (2003/33/EC)