Quantitative Analysis Of Major Elements In Coal And Heavy Metals Using Laser-induced Breakdown Spectroscopy

Elemental analysis of coal is significant in promoting the clean and efficient use of coal.Current methods for coal analysis are still time-consuming and require cumbersome sample preparation,making it difficult to meet industrial demand for elemental analysis of coal.Laser-induced breakdown spectroscopy(LIBS)is an optical method that has gained popularity in elemental analysis due to its ability to measure multiple elements simultaneously,ease of sample preparation,and rapidity.LIBS has great potential for coal analysis and heavy metal detection.However,conventional LIBS suffers from high detection limits and low sensitivity and accuracy,and cannot be widely used in industrial applications.Therefore,the sensitivity and accuracy of LIBS measurements of coal and soil have been improved and the elemental detection limits have been lowered by optimizing the LIBS system and introducing various quantitative analysis methods.The effects of laser parameters(wavelength,energy)and the ambient gas on coal plasma were investigated using a LIBS system.It was found that the 532 nm laser was more suitable for coal analysis,and the line intensity of C ? 247.86 nm could be effectively improved by Ar gas sweeping.The collinear double-pulse configuration was introduced to improve the measurement capability of coal analysis,and the effects of energy ratios and inter-pulse delay on the intensity enhancement of the elements C,H,O,Fe,Mg,Ca,Na and K were investigated.Good enhancement was obtained with an energy ratio of 20:100.The enhancement ratio of the line intensities was found to be related to the upper energy level of the spectral lines.In addition,the plasma temperature and plasma morphology were used to explore the enhancement mechanism of double-pulse LIBS.Four quantitative models based on PLSR,BPNN,SVR and RF algorithms were established for carbon content measurement of 65 coals,and found that the PLSR and BPNN models combined with double-pulse configuration can effectively improve the accuracy and precision.The heavy metal elements Zn,Cd,Cu,Ni,Pb in coal and soil were measured by the LIBS system,and the effects of ambient gas and double-pulse configuration on line intensity were investigated.The detection limits of heavy metals were calculated based on the linear regression curves of concentration and intensity under different experimental conditions(laser energy,selected spectral lines,ambient gas).The quantitative analysis of Cu was carried out using single-pulse LIBS and double-pulse LIBS combined with the normalization method,piecewise fitting method and the internal standard method,respectively.