The Assessment of Heavy Metals and Natural Radioactivity in the Phosphate Tailings at Minjingu Mines in Tanzania

Abstract

Extraction and processing of the phosphate rocks has produced a massive amount of waste and posed a significant environmental concern. The majority of wastes generated in the fertiliser industry are overburden or waste rocks from mining, and phosphate tailings (PTs) or phosphogyp-sum from the beneficiation process. Phosphate rock mining and beneficiation expose heavy metals and radionuclides into the environment, which are harmful to living things. The purpose of this study was to determine the concentration levels of heavy metals and radionuclides activity in the phosphate tailings at Minjingu mines in northen of Tanzania. Heavy metals content and radionu-clide activity concentration were determined using energy dispersive X-ray fluoresence spectroscopy (ED-XRF) and high pure garmin energy detector (HPGe), respectively. The concentra-tion of heavy metals investigated ranges: Cu – 12.9–27.3 mg·kg -1 , Fe – 7944.2–19052.2) mg·kg -1 , Mn – 410.9–474) mg·kg -1 , Ni – 1.9–13.2) mg·kg -1 , Al – 3597–13129.2) mg·kg -1 , Zn – 195.2–281.7) mg·kg -1 , Pb – 0.7–4.5) mg·kg -1 and As – 2.7–11.3) mg·kg -1 . The result revealed that, the concentration level of heavy metals (Cu, Fe, Ni, As, and Pb) are below the permissible level while concentration level for Zn has high concentration compared to permissible level limit. However, the activity concentration of radionuclides 226 Ra, 232 Th and 40 K were ranging from 311 to 7,606 Bqkg -1 , 207 to 654 Bqkg -1 and 131 to 762 Bqkg -1 , respectively. The reported results of activity concentration of radionuclides are found to be higher compared to the recommended world value. The study results will be used as a guide for decision making in addressing problems observed in phosphate tailings, including radiation safety standards for workers and environmental systems in phosphate mines.