The Speciation Analysis Of Heavy Metal In Coal Gangue And Releasing Mechanism Research

To make sure of the morphological structure and release mechanism of heavy metals contained in coal gangue, like Cr, Ni, Cu, As, Cd and Pb, and to ascertain the existing heavy-metal pollution to farmland soils neighboring coal gangue mines, the paper based the research objects on Zhongma Village Mine of Jiaozuo, Henan Province. With controlled studies of Xinxiang Zhaogu No.1 Mine and Xinmi Mi Village Mine, the morphology of heavy-metal elements contained in coal gangues from the three mines and from farmland soils(Zhongm Village Mine) were analyzed with BCR sequential extraction. And meanwhile, soaking and leaching experiments were conducted on the coal gangues, and the releasing law of heavy-metal elements contained in coal gangues during the soaking and leaching process was analyzed. What’s more, analysis was made of the relationship between the quantity of precipitated heavy metal during the soaking process and the content of exchangeable form. Main results are shown as follows:(1)The four elements Cr, Ni, Cd and As contained in the gangue samples from Zhongm Village Mine mainly existed in residual form; Pb mainly existed in residual form and reduction state; Cu mainly existed in residual form and oxidation state; There was no significant correlation between the gangue-particle size and the content and total quantity of effective forms of heavy metal in coal gangues. RAC method was adopted for ecological risk assessment. The assessment found that the exchangeable- form ratio of Ni and Cu contained in coal gangues from Zhongm Village Mine was 27.01 % and 21.41 % respectively, staying at moderate risk level. However, the exchangeable- form ratio of Ni and Cd contained in coal gangues from Mi Village Mine unexceptionally remained at moderate and high risks. And Pb, Ni and Cu contained in coal gangues from Zhaogu No.1 Mine were at moderate risk. It is shown by evaluation results of single pollution factors: mean value of heavy metals pollution coefficients of soil from the Zhong Ma Village are sorted: Cd> As> Pb> Cu> Ni> Cr, all samples of Cd elements have reached serious pollution levels, most samples of Pb and As have reached slight pollution, individual samples have reached moderate pollution.(2) According to one-day soaking experiment, the heavy metal Ni and As were more easy to be released in weak acid soaking solutions. Besides, there was no significant correlation between the gangue particle size fraction and the quantity of precipitated heavy metal after the coal gangue soaking. There was significant negative correlation between the release concentration of Cu, Ni and As contained in gangue samples from Zhongm Village Mine and the exchangeable-form quantity of heavy metals contained in gangues; however, the release concentration of Ni and Cd contained in gangues from Mi Village Mine was in positive correlation with their exchangeable-form quantity. Compared with China’s underground water quality standards, it is found out from the one-day immersion test results of waste rocks from the Zhong Ma Village, Mi Village and Zhaoguyi Mine, both the leaching concentrations of Ni and As elements exceed groundwater quality standards, there is a certain risk to the environment.(3) According to five-day soaking experiment, the heavy metal Cd in coal gangues was the most easily to be dissolved out, while Pb was the most difficult to be dissolved out. As far as the heavy-metal-element dissolution rate was concerned, it was sequenced in the following descending order: Cd> As> Cr> Ni> Cu≈Pb(Zhongma Village Mine); Cd> As> Cr> Ni> Cu> Pb(Zhaogu No.1 Mine); Cd> As> Cr> Ni> Cu> Pb(Mi Village Mine).(4)According to the leaching experiment, Ni, Cu, As and Cd unexceptionally saw the leaching release peak during the initial stage of the experiment. In addition, with the rise in time, the quantity of released heavy metals would gradually decrease and finally become steady. And fluctuation in leaching release occurred to both Pb and Cr.(5)The heavy metal As contained in coal gangues respectively from the three different mines share the maximum dissolution rate. The maximum dissolution rate of As contained in coal gangues from Mi Vilalge Mine ranked No.1, compared with that of Zhongma Village Mine and Zhaogu No.1 Mine, coming to 1.0844 %. With the maximum Cd dissolution rate of 0.0253 %, Zhongma Village Mine ranked the third. Pb contained in gangues from both Mi Vilalge Mine and Zhaogu No.1 Mine saw the poorest performance in dissolution rate.