Petrological and chemical characterizations of pristine and reworked phosphorites from Negev, Israel: Insights into industrial usage

Abstract

Phosphorites are an essential natural resource for producing phosphoric acid, phosphate fertilizers, and phosphate-based products. Detailed characterization and an appropriate assortment of phosphate resources are necessary to identify rocks that are chemically suitable for the phosphate industry. In the present study, we investigated the chemical composition and petrographic characteristics of phosphorites from three phosphate fields located in the same syncline, Zin Negev, Israel. At each site, the succession of pristine and reworked phosphorite layers along 10 m of the section was observed. Based on the chemical and petrographic analysis of phosphorites, it can be concluded that even though all the studied phosphorites were deposited in the same basin under suboxic conditions, the sedimentary settings are varied at each site. These variations resulted in differences in sedimentary structures and chemical composition, including the concentrations of major and trace elements and the abundance of the organic matter fractions. In all studied samples, a decrease in total organic carbon and redox-sensitive trace elements was observed upon the transition from a pristine to a reworked phosphorite phase, while the relative abundance of organic matter fractions remained nearly constant. The results of the present study indicate that, in addition to high-quality phosphorites at anticlinal heights, phosphorites with low organic matter contents in synclines can also be suitable for industrial applications. However, in phosphates, where humic substances represent the main fraction of OM that is located inside carbonate-fluorapatite grains, difficulties in the separation of OM from carbonate-fluorapatite grains during the production process cannot be excluded.