pH值对碱性煤矸石碱度和重金属释放规律影响研究

Study on effects of pH value on alkalinity and heavy metal release of alkaline coal gangue

为研究碱性煤矸石在不同pH值条件下碱度及重金属污染物的释放规律,以陕西省榆林市某矿区碱性煤矸石为研究对象,通过静态浸泡和动态淋滤试验,探究不同pH值条件下煤矸石中碱度与重金属元素Mn、Cu、Zn、Fe和Cr的释放规律。结果显示:在pH值为7,固液比(g∶mL)为1∶10条件下,煤矸石浸出液初始pH值为10.21,碱度释放量为0.154 mol/kg(碱度以H^(+)消耗量计);随pH值降低,煤矸石碱度释放能力增强,pH值为2时,碱度释放量增加至0.399 mol/kg;碱度释放具有明显的阶段性,在pH值为7的条件下,煤矸石碱度释放过程中前15.5 h为快速期,15.5 h后进入平稳期,快速释放期大约可释放总碱度的33.1%。结合煤矸石样品矿物成分及含量的XRD分析测试结果,本文阐明了碱度的释放机制。pH值对碱性煤矸石中重金属离子的释放同样有较大影响,pH值越低,重金属离子的释放率越高。当环境体系的pH值由7降至2时,Mn、Cu、Zn、Fe和Cr离子的释放率分别提升39.78%、37.83%、16.58%、11.20%与12.75%。动态淋滤试验结果表明:在淋滤液pH值为7,淋滤量为500 mL/次条件下,碱度和重金属离子的累积释放率均随淋滤次数的增加而增加,且碱度和重金属离子释放具有明显的异步效应。从矿区环境污染防控角度考虑,当煤矸石堆体环境体系中的pH>6时,各重金属元素的释放率相对较低,可有效减缓Mn、Cu、Zn、Fe和Cr离子对矿区环境的污染。

To study the release law of alkalinity and heavy metal pollutants of alkaline coal gangue under different pH values,the alkaline coal gangue in Yulin mining area,Shaanxi Province was selected as the research object.Through static immersion and dynamic leaching tests,the release law of alkalinity and heavy metal elements Mn,Cu,Zn,Fe,and Cr in coal gangue under different pH values was studied.The results show that when the pH value is 7 and the solid-liquid ratio is 1:10,the initial pH value of coal gangue leaching solution is 10.21 and the alkalinity release is 0.154 mol/kg(alkalinity is calculated by H^(+)consumption);with the decrease of pH value,the alkalinity release capacity of coal gangue increases.When the pH value is 2,the alkalinity release capacity increases to 0.399 mol/kg.The alkalinity release has obvious stages,under the condition of pH=7,the alkalinity in coal gangue in the first 15.5 h is the rapid release period,and enters the stable period after 15.5 h.The rapid release period can release about 33.1%of the total alkalinity.Combined with the XRD analysis results of mineral composition and content of coal gangue samples,the release mechanism of alkalinity is clarified.The pH value also has a great influence on the release of heavy metal ions in alkaline coal gangue.The lower the pH value,the higher the release rate of heavy metal ions.When the pH value of the environmental system is reduced from 7 to 2,the release rates of Mn,Cu,Zn,Fe,and Cr ions are increased by 39.78%,37.83%,16.58%,11.20%,and 12.75% respectively.The results of the dynamic leaching test show that when the pH value of the leaching solution is 7 and the leaching amount of 500 mL/time,the cumulative release rate of alkalinity and heavy metal ions increases with the leaching times,alkalinity and heavy metal ions release have an obvious asynchronous effect.From the perspective of environmental pollution prevention and control in the mining area,when the pH value in the environmental system of coal gangue pile is above 6,the release rate of each heavy metal element is relatively low,which can effectively reduce the pollution of Mn,Cu,Zn,Fe and Cr ions to the mining area environment.