油基岩屑焚烧过程中钡的转化与环境风险研究

Study on Barium Transformation and Environmental Risk during Oil-Based Drill Cuttings Incineration

油基岩屑焚烧处置技术已被广泛应用,为探究油基岩屑焚烧尾渣的主要环境风险及其形成机制,有效防控油基岩屑利用处置环境风险,通过实际样品采集和实验室模拟等方式,结合XRD、SEM-EDS、同步热分析等多种表征方法,针对四川省天然气开采油基岩屑典型回转窑焚烧处置过程中钡的转化以及焚烧尾渣的环境风险特征开展了研究.结果表明:钡是油基岩屑中的主要重金属,油基岩屑经焚烧后,尾渣中钡的酸浸浸出毒性水平大幅上升,平均值达到333.0 mg/L,超过《危险废物鉴别标准浸出毒性鉴别》(GB 5085.3—2007)标准限值;在还原气氛下,800℃时模拟焚烧尾渣可交换态钡含量和钡的酸浸浸出毒性水平出现大幅上升,平均值分别达到8675.74 mg/kg和244.38 mg/L,并在1100℃时进一步上升,不同油基岩屑的浸出毒性发生这种跃升的温度条件存在差异.这种现象产生的主要原因是油基岩屑中的硫酸钡在800℃以上会发生碳热还原反应生成硫化钡,并与氯化氢等反应产生氯化钡,这种还原转化过程主要发生在硫酸钡晶体颗粒表面,并最终形成了被可溶性钡外壳包裹的硫酸钡晶体颗粒.研究显示,可溶性钡是油基岩屑焚烧尾渣的主要环境风险,其产生主要与硫酸钡的碳热还原反应有关,钻井岩屑还原性高温热处理过程产生的可溶性钡环境风险应得到广泛关注和有效防控,建议从标准政策制定、风险源头防控和尾渣末端治理等方面进行控制.

The incineration technology of oil-based drill cuttings has been widely used.In order to effectively control the environmental risks in the utilization and disposal of oil-based drill cuttings,the main environmental risks and formation mechanisms of the incineration tailings of oil-based drill cuttings were explored.This study investigated the conversion of barium and the environmental risk characteristics of incineration tailings in typical rotary kiln incineration disposal process of oil-based drill cuttings from natural gas exploitation in Sichuan Province.Various characterization methods such as XRD,SEM-EDS,and simultaneous thermal analysis were used,including actual sample collection and laboratory simulations.The results indicated that barium was the main heavy metal in oilbased drill cuttings.After incineration of oil-based drill cuttings,the acid leaching toxicity of barium in the tailings increased significantly,with an average value of 333.0 mg/L,which exceeded the corresponding limit.In reducing atmosphere,the exchangeable state and extraction toxicity by acid leaching of barium from simulated incineration tailings increased significantly at 800℃,with the average values reaching 8675.74 mg/kg and 244.38 mg/L,respectively.These values further increased at 1100℃.The temperature conditions under which this extraction toxicity jump occurs varied among different oil-based drill cuttings.The main reason for this phenomenon was that the barium sulfate in oil-based drill cuttings was transformed into barium sulfide through carbothermic reduction reaction above 800℃,and reacted with hydrogen chloride to form barium chloride.This reduction conversion process mainly occurred on the surface of barium sulfate crystal particles,and eventually formed barium sulfate crystal particles with soluble barium shells.The research shows the soluble barium is the main environmental risk of incineration tailings of oil-based drill cuttings,which is mainly related to the carbothermal reduction reaction of barium sulfate.The environmental risk of soluble barium from the reductive high-temperature heat treatment processes of drilling cuttings should be widely concerned and effectively prevented.It is recommended that standard policy development,risk source prevention and tailing end treatment should be used for control.