Research On Soil Heavy Metal Detection Technology Based On Laser-induced Breakdown Spectroscopy

The detection of heavy metal pollution in the soil is intuitively important for soil evaluation and pollution prevention.With its real-time and rapid advantages,laser-induced breakdown spectroscopy technology can already be applied to the field of soil heavy metal detection.This paper studies,designs and manufactures a portable LIBS instrument,builds a LIBS experimental platform,discusses the configuration and method of experimental samples,and studies the LIBS signal enhancement method,and uses random forest algorithm to quantitatively analyze and detect heavy metal elements in the soil.Developed LIBS portable instrument hardware system and supporting software.Realize the real-time detection of heavy metals in soil by LIBS instrument.The main work and research results of this paper are as follows:(1)Developed LIBS portable instrument hardware system and supporting software.the corresponding optical path design is carried out,and the hardware system of the portable instrument is designed with 3D drawing software.At the same time,the instrument selection and assembly are carried out,and the integration of the portable instrument is finally completed.Then,according to the characteristics of the instrument,the supporting software was designed.The designed software has the functions of setting LIBS experimental parameters,real-time spectrum acquisition,display and storage,and quantitative analysis of spectrum data and display the quantitative accuracy.Finally,a complete test of the portable instrument was carried out.The standard deviation was less than 10%,and the detection limit was far less than 300 ppm.The test results fully met the subject requirements.(2)The double-pulse LIBS experimental platform was built,the overall structure and optical system were designed,and the experimental devices were selected.Research on double pulse signal enhancement methods.The LIBS spectrum signal obtained by the double pulse technology is enhanced,and the influence of the parameters of the double pulse LIBS experiment system(laser beam interval time,laser pulse energy,spectrum acquisition delay)on the spectrum signal intensity is discussed,and the soil LIBS simulation experiment is determined The experimental conditions used are: vertical laser energy 30 m J,horizontal laser energy 100 m J,two laser beam interval time 6μs,spectrum acquisition delay 0.25μs.(3)The soil samples with different concentrations of heavy metal elements were configured,and the spectral information of the soil was analyzed,and the characteristic lines of the three elements Ni,Cu,and Pb were selected.Using LIBS and chemometric methods to carry out geometric quantitative analysis of the content of heavy metal elements in the soil.By optimizing the number of ntree: decision trees and mtry: the number of randomly selected attributes,the random forest algorithm is used to quantitatively analyze the optimized spectral data to obtain the content of heavy metal elements in the soil.Comparing the double-pulse quantitative results with the single-pulse quantitative results,it can be concluded from the linear fitting correlation,root mean square error and relative error that the double-pulse detection accuracy is better than the single-pulse detection accuracy,and the double-pulse detection is calculated.The limit is much lower than single pulse.This paper successfully developed a portable instrument capable of detecting heavy metal elements in the soil,and further studied the signal enhancement method.It proved the feasibility of LIBS technology in the detection of metals in the soil.Through the production of LIBS portable instruments,it was proved that LIBS technology can be applied to the field analysis of soil heavy metal content detection.