Preparation Of Bismuth-Based Photocatalytic Materials And Their Degradation Of Waste Polymer Water-Based Drilling Fluid

In China,the annual quantity of waste drilling fluid generated from drilling operations exceeds 1×10⁷m³.Among these fluids,waste polymer-water-based drilling fluids exhibit characteristics such as low recycling rate,high stability,and difficulty in removal.The effective elimination of residual components like polymer additives and heavy metal ions has always been a significant and challenging aspect during the treatment process of waste polymer-based drilling fluids.Photocatalytic technology offers an efficient solution to address environmental pollution problems by virtue of its advantages,including selective degradation of organic molecules and reduction of heavy metal ions,reusability,and absence of secondary pollution.Leveraging the benefits of photocatalysis technology in treating polymer molecules and heavy metal ions,it has been introduced innovatively into the field of waste polymer-water-based drilling fluid treatment.The development of high-performance photocatalytic materials is the key to the photocatalytic treatment of waste polymer-water-based drilling fluids.Among the various photocatalytic materials available,Bi OX semiconductor materials have gained wide popularity due to their unique layered structure,suitable band structure,and chemical and optical stability.In this study,Bi OBr_0.5Cl_0.5 solid solution was synthesized as the first setp by controlling the preparation methods and reaction parameters.To address the challenges of low quantum efficiency and fast electron-hole recombination rate of Bi OBr_1-yCl_y solid solution,metal and non-metal modifications were carried out resulting in the synthesis of two photocatalytic materials:Bi/Bi OBr_0.5Cl_0.5-0.3 and 0.5S-Bi OBr_0.5Cl_0.5.These materials effectively resolved the issues mentioned,thereby providing high-performance photocatalysis materials for the degradation of waste polymer-water-based drilling fluids through photocatalysis.Bi/BiOBr_0.5Cl_0.5-0.3 and 0.5S-BiOBr_0.5Cl_0.5 were utilized to degrade four types of drilling fluid polymer additives:K-PAM encapsulant,FA367 encapsulant,PAC-LV fluid loss reducer,and HEC viscosifier.The reduction of two heavy metal ions,Hg²⁺and Cr⁶⁺,was also investigated.Experiment results demonstrated that both materials achieved COD removal rates exceeding 79%for all four polymer additives.The reduction rates for Hg²⁺exceeded 37%,while for Cr⁶⁺,they surpassed 89%.Additionally,a detailed analysis of the degradation and reduction mechanisms was conducted.Building upon the successful treatment of polymer drilling fluid additives and heavy metal ions using Bi/Bi OBr_0.5Cl_0.5-0.3 and 0.5S-Bi OCl_0.5Br_0.5 photocatalytic materials,the degradation of three types of field-discarded polymer-based drilling fluids was carried out.These fluids were collected from unstable formation layers,directional drilling sections,and deep formation layers.After degradation,all three fluid systems exhibited a reduction in apparent viscosity of over 65%,a decrease in suspended solids（SS）content by more than 67%,COD removal rates exceeding 49%,Hg²⁺reduction rates surpassing77%,and Cr⁶⁺reduction rates reaching over 74%.This study presents a novel approach to treating waste polymer-water-based drilling fluids by synthesizing two new efficient photocatalyst materials through modifications of Bi OBr_1-yCly solid solution.It offers new insights and methods for the treatment of such drilling fluids.