_applied sciences_  
_Article_  
**Portable X-ray Fluorescence (pXRF) as a Tool for Environmental Characterisation and Management of Mining Wastes:**  
**Benefits and Limits**  
**[PERSON] \({}^{1,*}\)\({}^{\copyright}\)**, [PERSON] \({}^{1}\), [PERSON] \({}^{1,2}\)\({}^{\copyright}\), [PERSON] \({}^{3}\)\({}^{\copyright}\), [PERSON] \({}^{3}\)\({}^{\copyright}\),  
**[PERSON] \({}^{1}\)\({}^{\copyright}\), [PERSON] \({}^{4}\)\({}^{\copyright}\) and [PERSON] \({}^{1}\)\({}^{\copyright}\)**  
\({}^{1}\)  
remote regions, providing cost-effective technology for real-time data, especially when immediate action is needed as a result of environmental disasters [6]. The description of the technique and its applications have been reported in several studies and reviews [5; 7; 8]. Portable XRF offers many advantages and few disadvantages compared to conventional laboratory analysis of environmental samples. Sensitivity to trace element variations is one of the strong points of pXRF. However, there are possible pitfalls when a new pXRF instrument is employed, and it is worth focusing on the possible errors that occur during pXRF analyses since these instruments can be easily used by any operator. The limit of detection (LOD) varies with different analysers and measurement time. Overall, the best instruments are capable of a LOD in the 5 to 100 mg/kg range for elements with an atomic number (Z) between 19 (K) and 68 (Pb). Hence, pXRF is not suitable for analysing very low concentrations although the sensitivity can vary among different analytes. For most of the elements of environmental concern, pXRF may not be capable of discriminating values above or below national regulatory threshold levels (e.g., in soils, for public, private, and residential use, the limit for Hg is fixed at 1 mg/kg according to Italian Legislative Decree 152/2006 [9]). However, this technique is particularly useful in the detection of samples with \"anomalous\" high concentrations with respect to background levels or weakly impacted environmental areas. Based on pXRF analysis on large datasets, a subset of samples can be selected for further analyses such as, for instance, mineralogical, compositional, or related to the speciation of potentially toxic elements (PTEs). Otherwise, old mining wastes with exceptional high metal concentrations can be identified for potential reprocessing. Thus, the extraction of valuable elements would be followed by the mitigation of dispersion of the contaminant and ecological or health risks. However, to achieve the best overall results, pXRF data should be validated using conventional laboratory-based spectrometric techniques, and geochemical expertise is required for the reliable interpretation of pXRF data. This is especially important since pXRF can over- or underestimate concentrations as well as detect false positives, with varying levels of accuracy for different elements. The handling of the sample prior to pXRF analysis greatly affects the accuracy of the technique. Variations in soil moisture, particle size, heterogeneity, and density directly affect the accuracy of the results. For instance, [PERSON] and [PERSON] [10] found that sample preparation could lead to more significant errors than the use of different pXRF instruments. When the sample preparation procedure is the same as the laboratory standard procedures, and the sample is sieved, dried, milled, and homogenised (\"lab-prepared samples\"), pXRF can provide accurate results comparable to destructive standard laboratory analyses (e.g., ICP-OES, ICP-MS), hereafter referred to as \"laboratory analyses\" [5; 6; 11]. However, the standard procedure can be so time-consuming that pXRF analysis on lab-prepared samples may not be cost-effective, as the gain in accuracy is followed by a reduction in the geochemical dataset. The last issue affecting pXRF analyses is related to interferences and matrix effects. Interferences among elements can be produced by overlaps of the characteristic X-ray emission lines.