Volumetric characterisation of waste deposits generated during the production of fertiliser derived from phosphoric rock by using LiDAR and electrical resistivity tomography.

The lack of environmental regulations before 1998 brought about significant ecological consequences in Europe. There are 4,000,000 ha potentially contaminated by waste, resulting from industrial activity. These sites present abnormal values of salinity, alkalinity, and organic and inorganic pollutants. A representative example of this is the production of fertiliser derived from phosphoric rock through the wet acid process which mainly produces phosphogypsum and pyrite ashes. For each tonne of fertiliser produced, five tonnes of phosphogypsum are generated, which in most of the cases were simply piled into non-conditionate deposits; currently, there is no information about these deposits. Hence, fast and affordable methodologies should be developed to calculate the volume contained in the existing waste deposits. Thus, this study aims to: i) scan the industrial area selected in order to identify the distribution and possible variants of the waste that make up the configuration of geoelectrical profiles and boreholes, and ii) accurately determine the volume contained in the chosen deposits by merging Electrical Resistivity Tomography with LiDAR point cloud. Results show a range of deposit volumes that run from 4900 m to 59,300 m. The density of LiDAR point cloud (1 point/m) ensures metric precision for the superficial layer. The Electrical Resistivity Tomography revealed the geometry of the deposits that superposes two layers marking the border between waste and natural terrain, and the boreholes guarantee the exactness of the waste layer thickness. This synergistic combination of Electrical Resistivity Tomography with LiDAR point cloud yields an accurate method that we used to calculate the volume of waste present in the deposits.