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

Mdachi Daniel D., Rugaika Anita M., Machunda Revocatus L.

Journal of Ecological Engineering

2024

Vol. 25, nr 1

269--277

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 concentration 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 226Ra, 232Th and 40K 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.

Optimization of flotation efficiency of phosphate minerals in mine tailings using polymeric depressants : experiments and machine learning

Alsafasfeh Ashraf, Alagha Lana, Alzidaneen Ala, Nadendla Venkata Sriram Siddhardh

Physicochemical Problems of Mineral Processing

2022

Vol. 58, iss. 4

art. no. 150477

In this study, direct froth flotation experiments were conducted on silicate-rich phosphate tailing samples. The average grade of P2O5 in the flotation feed was 21.6% as determined using a combination of spectroscopic techniques including X-ray powder diffraction (XRD), mineral liberation analysis (MLA), and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS). Two polymers were selected to promote the depression of silicates and enhance the flotation of phosphates: in-house synthesized hybrid polyacrylamide (Hy-PAM) and chitosan. Flotation efficiency of phosphates was evaluated at different flotation conditions including depressant type, depressant dosage, pH, and the flotation time. Results indicated that the optimum flotation efficiency of phosphate minerals (84.6% recovery at 28.6% grade of P2O5) was obtained when Hy-PAM was utilized at the studied range of pH and flotation time. All datasets produced from the flotation experiments were integrated within the framework of machine learning (ML) using artificial neural networks (ANNs). The ANN platform was trained, validated, and successfully employed to predict the process outcomes in relation to the pulp and reagents characteristics, which in turn were used to determine the optimum values of process variables. Coefficient of determination (R2), mean absolute error (MAE), and root-mean-square error (RMSE) were used as model indicators. Optimization results showed that the peak flotation performance could be achieved at higher dosages of both polymers. However, lower pH and shorter flotation time for Hy-PAM, and higher pH and longer flotation time for chitosan, were predicted to give the optimum process efficiency.