Simulation Experiment Study On The Bedding Oxidation-acid Eroded Reaction Of Black Shale

The interlayer oxidation-acid erosion of black shale is a kind of water-rock chemical weathering.Because of the black shale is rich in sulfide minerals and organic matter,the weathering process of the black shale is greatly different from that of other types of rock.With the increase of engineering activities in various industries in China,a series of engineering geological disasters caused by oxidation-acid erosion of black shale has also increased.The Xujiaping landslide in this paper is in an understable state under the oxidation acid erosion of the black shale,which eventually leads to the landslide.Therefore,it is of great significance to study the evaluation and prediction of engineering geological disasters by the study of the effect of black shale on the oxidation-acid corrosion.This paper takes the black shale in Xujiaping area as the research object,and understands the geochemical characteristics of black shale by means of field investigation,sampling and indoor rock identification.According to the characteristics of the slope body structure of Xujiaping landslide and the characteristics of apparent pHenomena in the process of interlayer oxidation-acid etching,the bedding oxidation-acid etching reaction model of the field black shale is simplified,and simulate the bedding oxidation-acid erosion of black shale by the self-designed interlayer oxidation-acid erosion test device,finally reveal the mechanism of the interlayer oxidation-acid erosion of black shale.The following results are obtained through research:(1)The geochemical characteristics of black shale and limestone in the study area were analyzed by X-ray diffraction(XRD),X-ray fluorescence spectrometer(XRF)and SEM-EDS.The results show that black shale mainly contains quartz,feldspar,clay minerals,pyrite and a small amount of carbonate minerals.The main mineral compositions of limestone are calcite and dolomite.The microstructure of fresh shale is dense,in which that the quartz and feldspar form a large grain skeleton and the clay minerals are attached to the surface of the large frame particles or fill in the micropores,clay minerals existing in the form of sheets and sheets.The microstructure of limestone is also dense,mainly composed of grain-dominated crystal.(2)In this paper,the evolution sequence characteristics of the weathering products of the sulfide minerals in the black shale are obtained by simulating the interlayer oxidation-acid etching process.During the experiment,pH value of oxidation-acid etching solution in the first cycle changes significantly,as the experiment progresses,solution pH change more slowly,and finally tends to be stable,the EC cycle constantly on the rise,and finally tends to be stable.The ORP and dissolved oxygen of aqueous solution have similar regularity and characteristics,and the linear positive correlation between ORP and dissolved oxygen is obtained through data analysis.In addition,The types of elements in the oxidation-acid etching solution are basically the same as those of the chemical composition and mineral composition of the corresponding experimental sample.The variation characteristics of each element in the oxidation-acid etching solution are also consistent with the experimental expected results.(3)Mechanisms of oxidation-acid etching of black shale include the oxidation of pyrite,silicate mineral acid corrosion,dissolution of carbonate minerals,salts crystallization and the transition between unstable clay minerals content.