Investigation of Cd contents in several phosphate rocks used for the production of fertilizer

Abstract

Phosphate rocks (PRs) can be a source of cadmium pollution in soil and food chain. PRs are mainly used for the manufacturing of phosphate fertilizers. The characteristics of PRs with special reference to cadmium, which are important phosphate fertilizer source, were investigated. In my field of study, PR of USA (PR1: from Wyoming, PR2: from Florida PR3: from Idaho), Morocco (PR4: from Qued Zem), Russia (PR5 from Slyudanka), and Japan (PR6: from Okinawa) were selected and compared using X-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS) and X-ray diffraction (XRD). Elemental analysis results of PR samples showed that they were mainly composed of Ca, P, Si, Al, S and Fe. Total phosphate concentration in all PRs was 6 to 38% on the average. The Cd concentration levels in all PR samples ranged from 0.15 to 507mgkg−1. PR4 sample exhibited about two times higher Cd concentration than those of the literatures so far published. XRD analysis revealed that; fluorapatite ((Ca5(PO4)3)F), hydroxyapatite (Ca10(PO4)6(OH)2) and carbonate fluorapatite (Ca5(PO4,CO3)3F) were the dominant minerals. This study also confirmed that PR3 and PR4 exhibited higher Cd content and prominent mineral component was carbonate fluorapatite, suggesting that Cd might be exchanged to Ca and/or occluded in carbonate fluorapatite during its formation by sedimentation.