Preparation Technique Of Lightweight Aggregates From Shale Gas Oil-drilling Cuttings

Oil-drilling cuttings have been continuing to increase along with the large-scale exploitation of shale gas.The surface of oil-drilling cuttings contains a large amount of oil pollutants,which are flammable and difficult to degrade in the environment.In order to decreasing the serious threat to the environment and human health,multiple harmless treatment methods for oil-drilling cuttings have been developed,but resource utilization was rarely involved.How to convert them into valuable products is an important challenge currently facing.Lightweight aggregates have a wide range of applications in construction,roadbeds,bridges and other fields due to its unique characteristics of light weight,high strength and low water absorption.However,few scholars have studied the preparation lightweight aggregates from oil-drilling cuttings.Based on the analysis of the characteristics of the oil-drilling cuttings after deep desorption treatment,this paper chose the oil-drilling cuttings and fly ash to prepare the non-sintered aggregates and sintered aggregates.In addition,low-temperature sintered aggregates were prepared by adding borax pentahydrate as flux to reduce energy consumption.These provide certain theoretical and applied research foundation for realizing the resource utilization,expanding the research and industrial application of oil-drilling cuttings in aggregates.In the preparation of non-sintered aggregates,the effects of different raw materials and the amount of sodium silicate on the cylinder compressive strength,water absorption and densities of non-sintered aggregates were discussed.Meanwhile,preparation technique of non-sintered aggregates was defined by combining the microcosmic analyses,such as XRD,FT-IR and SEM.The results showed that under the optimized experimental condition with the mixing ratio of 4:6 in fly ash and oil-drilling cuttings,and adding 75 g water glass in 500 g ground mixture,we could obtain high-performance non-sintered aggregates with cylinder compressive strength of 5.1 MPa,water absorption of 8.57%,apparent density of 1993.0 kg/m³and bulk density of 870.5 kg·m^-3.Compared with the non-sintered aggregates with other raw materials and water glass content,the non-sintered aggregates have better physical properties with high strength,low water absorption and low density.From the analysis of the mineral phase,molecular structure and microstructure,it can be known that water glass provided an alkaline environment for mixture powder,which could destroy the glass body in fly ash,release silicon-aluminum active materials and accelerate the hydration reaction process of calcium oxide,sulfate and silicon-aluminum.All the preferred aggregates with different mixing ratios of raw material produced amorphous gel.In contrast,the non-sintered aggregates under the optimal parameters had the fewer unexcited glass microbeads,more tightly and evenly hydration products.In the preparation of sintered aggregates,the influence of sintering temperature and sintering time on the performances of aggregates were investigated.Combined the phase analysis from XRD,the optimal sintering system was determined.The results showed that proper sintering temperature and sintering time can help to the formation and strength of new crystalline phases,resulting in effectively increase of the cylinder pressure strength.The generated pores contributed to obtaining a lower density.However,once they exceed a certain limit,pores in the sintered lightweight aggregates are prone to merge,and the aggregates are easy to adhesion,resulting in the poor molding degree.It had negatively effects on the cylinder compressive strength.Based on comprehensive consideration,the optimal preparation conditions for sintered lightweight aggregates from oil-drilling cuttings were determined to be sintering temperature of 1145°C and sintering time of 30 min.In terms of the obtained sintered aggregates,the surface was a smooth and dense enamel layer,and the interior distributed a large number of uniformly pores,crystalline phase,such as diopside,augite,the ceramic phase nepheline and feldspar minerals.A small density and excellent mechanical properties were obtained.In addition,we obtained high-performance sintered aggregates with cylinder compressive strength of 8.6 MPa,water absorption of 3.77%,apparent density of 1853.9 kg·m^-3and bulk density of 850.2 kg·m^-3,which met the requirements of national standard GB/T17431.1-2010 for high-strength lightweight aggregate at class 800.In the preparation of sintered aggregates from borax pentahydrate and oil-drilling cuttings,we explored the sintering temperatures with borax pentahydrate as the flux.Furthermore,the optimal sintering temperature and the effect of borax pentahydrate on the sintering temperature of aggregates were clarified by combining with XRD.The results showed that borax pentahydrate has a comparatively large impact on the sintered temperature of aggregates.After adding borax pentahydrate,the sintering temperature at 875°C can obtain low-temperature sintered aggregates with density of class 800 and a cylinder pressure strength of 8.9 MPa,which met the requirement of national standard GB/T 17431.1-2010 for high-strength lightweight aggregates under class 800.Borax pentahydrate contains a large amount of B₂O₃and Na₂O,which can reduce the softening temperature of the sample.It contributed to producing a low-viscosity liquid phase at a lower temperature for sintered aggregates,effectively reducing the sintering temperature and realizing the preparation of low-temperature sintered aggregates.The crystal phases such as nepheline,diopside and calcium feldspar were distributed inside the sample,which was helpful to strength development.Converting oil-drilling cuttings into lightweight aggregates,whether non-sintered aggregates or sintered aggregates,could reduce secondary pollution and realize the utilization of waste resources.If lightweight aggregates are applied to construction,roadbed and other fields,the processing speed of oil-drilling cuttings would be improved,which have potential economy,environmental and social benefits.