Research And Development Of Equipment For In-situ Detection Of Heavy Metal Contamination In Soil By LIBS

Rapid in-situ detection of heavy metals in soil is essential for soil remediation and pollution monitoring.Simultaneous analysis of heavy metals in soil using traditional methods is very difficult,not only is it labor intensive but also has an impact on the health of the experimenter.Laser induced breakdown spectroscopy is a rapidly developing technique for chemical elemental analysis in recent years.It has the advantages of real-time,rapid,on-site detection and simultaneous detection of multiple elements.It can provide technical support for environmental improvement and soil heavy metal pollution management in China,and promote sustainable green and benign development.Therefore,the research and development of in-situ soil heavy metal pollution detection technology and equipment based on LIBS technology has important application value.This paper focuses on the technical bottleneck in the quantitative in-situ analysis of soil heavy metals based on LIBS technology,and the algorithm research to improve the quantitative analysis capability of this technology.The main research results are as follows:(1)Study on detection parameters and spectral pre-processing of LIBS technique.The characteristics of the LIBS technique for the detection and analysis of different heavy metal contaminants were investigated.The experimental parameters such as analytical wavelength,reference wavelength,excitation energy and number of excitation points for each element were determined,and the preparation process of soil standard samples was explored and determined.The data stability and pre-processing methods for spectral data acquisition were investigated,and preliminary qualitative analysis of soil spectra was carried out.A solid foundation was laid for the next step of quantitative analysis.(2)A model based on partial least squares non-linear regression method was developed for the quantitative analysis of soil heavy metals.Taking Hg and Cd elements as examples,the effects of matrix elements on the quantitative analysis of heavy metals in soil were considered in the context of atomic spectroscopy and the matrix effect of soil.The results showed that the presence of matrix elements Ca and Fe affected the quantitative analysis accuracy of Hg and Cd,respectively.The accuracy of the quantitative analysis models for Hg and Cd with the addition of matrix elements by partial least squares non-linear regression was greatly improved,with the relative errors of concentration prediction reduced from 16% and 13.62% to5.92% and 8.01% respectively.This indicates that the model can better explain the relationship between spectral information and elemental concentrations.(3)A model for the quantitative analysis of heavy metals in aqueous soils based on the ablation factor was developed.A partial least squares regression method was used to establish the moisture content prediction model,and the correlation coefficient of predicted water content reached above 0.99,and the root mean square error of prediction(RMSEP)was only 1.3%.By analyzing the effect of the moisture content of the sample on the laser ablation,the correlation between the laser ablation factor and the moisture content of the sample was determined in conjunction with the experiments.A quantitative analysis model based on the ablation factor was developed for aqueous samples,and the correlation coefficient of the model reached0.98.The quantitative analysis model was validated for the heavy metals Cu and Cr in the samples by both weighing and direct measurement,and the relative error of concentration prediction was within 10%,with an accuracy improvement of more than 80%.(4)Development of mobile LIBS equipment.Based on the characteristics of laser induced breakdown spectroscopy for the detection and analysis of heavy metal contaminants in soil.Research on effective ways to improve its detection and analysis capabilities.To develop a mobile LIBS equipment that can perform real-time,rapid,on-site detection of heavy metal contaminants in soil.It can meet the needs of high precision and low detection limit field analysis of heavy metals in soils.The upper computer control and analysis software was also written.The automatic control of the LIBS instrument was realized.It provides technical support for the rapid quantitative analysis of heavy metal elements in soil.(5)The practical application of mobile LIBS equipment was investigated.The mobile LIBS equipment was used to detect and assess the heavy metal contamination of a gold mine soil.The mobile LIBS analysis was fast,with results coming out in as little as two minutes from sample flattening to quantitative analysis,which can realize the analytical needs of in situ rapid monitoring of soil heavy metal contamination.The press-flat method was used to prepare cement samples for the analysis of metal oxides in cement.The relative errors of the model predictions are basically within 1% and the prediction results are good.The simplicity of the sample preparation process by the flattening method and the ease of automated operation in an assembly line suggest that the LIBS technique has greater potential for the on-line measurement of cement powders.The paper addresses the problems that LIBS technology has in the field of in-situ detection of heavy metal pollution in soil,such as the inability to analyze in-situ,the poor precision of quantitative analysis and the inability to directly analyze water-bearing soil.Based on the construction of mobile LIBS detection equipment,the paper carried out research on quantitative analysis methods and direct quantitative analysis models for aqueous soils.A set of mobile LIBS equipment was developed for the in-situ and rapid detection of heavy metal contaminants in soil.A quantitative analysis method based on partial least squares non-linear regression method and a quantitative analysis model for heavy metals in aqueous soils based on ablation factor were established,providing technical support for in-situ soil heavy metal detection.