Prediction of As, Cd, Cr, Hg, Ni, and Se Concentrations in Organic Amendments Using Portable X-ray Fluorescence and Multivariate Modeling

Portable X-ray Fluorescence Analysis of Organic Amendments: A Review

Portable XRF spectrometry (pXRF) has recently undergone significant technological improvements and is being applied in a wide range of studies. Despite pXRF advantages, this technique has rarely been used to characterize organic amendments and residues. This article reviews those studies undertaken to date in which pXRF is used to characterize these products. Published studies show that pXRF correctly measures elements such as Fe, Pb, Zn, Mn, Ca, and K but gives conflicting results for elements such as Cr, Ni, and As. Among the reasons that may cause the low performance of the technique with certain elements or under certain measurement conditions would be the inadequacy of the analytical comparison procedures used (i.e., digestion with aqua regia), the lack of knowledge of the interfering effects of organic matter, and sample moisture on the XRF signals and the need for a standardized protocol for performing the measurements. However, the speed and low cost of the procedure forecast a greater future use of this technique, especially in cooperation with other fast spectroscopic techniques based on near-infrared (NIRS) or mid-infrared (MIR) spectroscopies. Chemometric procedures based on one or more of these techniques will allow the prediction of elements below the detection limit of pXRF instruments (Cd, Hg), or other properties of organic amendments (organic matter, N, electrical conductivity, cation exchange capacity).

pXRF on printed circuit boards: Methodology, applications, and challenges

In order to develop methods to determine the chemical composition of Waste Printed Circuit Boards (WPCB), this study focused on the analysis of 10 metals (Cu, Fe, Sn, Zn, Pb, Ni, Sb, Cr, Mo and Pd) using portable X-ray fluorescence (pXRF) compared to ICP-MS measurements after aqua regia digestion. Different experimental conditions were tested: 3 particle sizes (200 µm, 750 µm and 2 mm) and 3 sample preparations (tube, cup and loose powder). For each condition tested, 8-16 independent replicates were done. ICP measurements with the 200 µm sample, considered as the reference condition in this study, confirmed the homogeneity of the sample at this particle size and the robustness of the sampling protocol (RSD < 5% for all elements). For this particle size, pXRF has low data dispersion too (Cu, Fe, Sn, Zn, Pb, Sb and Cr showed RSD < 10%) and the use of loose powder seems to be a sufficient preparatory step. Moreover, the deviation of pXRF measurements with the 200 µm sample from the reference condition was acceptable (<20%) for Cu, Sn, Zn, Pb, Ni, Sb and Mo. For coarser samples, i.e. 750 µm and 2 mm, the homogeneity was much more doubtful, which needs to be offset by a larger number of repetitions. For these particles sizes, pXRF set to factory-installed mining mode did not produce accurate measurements but could provide a rapid non-intrusive approach for first-level screening to assess the relative difference of metal contents between WPCB samples.

Impact of Biochar Amendment on Soil Properties and Organic Matter Composition in Trace Element-Contaminated Soil

The application of biochar as an organic amendment in polluted soils can facilitate their recovery by reducing the availability of contaminants. In the present work, the effect of biochar application to acid soils contaminated by heavy metal spillage is studied to assess its effect on the quantity and composition of soil organic matter (SOM), with special attention given to soil humic acids (HAs). This effect is poorly known and of great importance, as HA is one of the most active components of SOM. The field experiment was carried out in 12 field plots of fluvisols, with moderate and high contamination by trace elements (called MAS and AS, respectively), that are located in the Guadiamar Green Corridor (SW Spain), which were amended with 8 Mg·ha⁻¹ of olive pit biochar (OB) and rice husk biochar (RB). The results indicate that 22 months after biochar application, a noticeable increase in soil water holding capacity, total organic carbon content, and soil pH were observed. The amounts of oxidisable carbon (C) and extracted HAs in the soils were not altered due to biochar addition. Thermogravimetric analyses of HAs showed an increase in the abundance of the most thermostable OM fraction of the MAS (375–650 °C), whereas the HAs of AS were enriched in the intermediate fraction (200–375 °C). Spectroscopic and chromatographic analyses indicate that the addition of biochar did not alter the composition of the organic fraction of HAs, while Cu, Fe, and as were considerably accumulated at HAs.