Trace metal elements in phosphate rock wastes from the Djebel Onk mining area (Tébessa, eastern Algeria): A geochemical study and environmental implications

Algeria is one of the phosphate-rich countries where many deposits are found in the Tébessa region which are currently being mined from the Kef Essenoun quarries. The processing of run-off-mine, to increase P2O5 grads in the commercial product, includes the use of wet and dry procedures which in turn leads to the production of large amounts of wastes. The present study focuses on tracking the amount of trace metal elements (TMe) in the phosphate rock wastes resulting from the processing of phosphate run-of-mine. The representative samples of solid rejects and sludge wastes from both processing ways were collected and analysed using SEM and FTIR to characterise the materials, whereas ICP-AES and ICP-MS were used to determine major and TMe compositions, respectively. The results showed that the analysed wastes are P-enriched (P2O5 = 20 wt% - 27 wt %) together with similar mineralogy such as natural phosphorites (carbonate fluor-apatite), but they displayed an enhancement in matrix phases. Moreover, the overall tendency showed that the concentrations of TMe are relatively increased with a decrease in grain size diameter where higher contents of V, Cr, Co, Ni, Cu, Zn, As, Zr, Nb and Cd have been recorded in sludge and fine fraction from the wet way process (Rw −0.08 mm) when compared to other samples. The fine fractions generally contain the matrix that enhances almost all of TMe except for Sr and U which are hosted in apatite. Risk assessment of TMe showed that both raw phosphorites and their wastes, as all worldwide sedimentary phosphorites, yield some hazardous TMe exceeding the standards for soils (e.g., U, Cd, Cr, Mo, V and Tl). Hence, owing to the waste exposure and mobilisation of the finest particles by wind and rainfall, these hazardous metals could have harmful effects on the environment as well as human health. © 2021 Elsevier Ltd