Selectivty Assessments of a Sequential Extraction Procedure for Potential Trace Metals’ Mobility and Bioavailability in Phosphate Rocks from Jordan Phosphate Mines

Abstract

A modified six-step sequential extraction procedure was used to fractionate and determine the following trace metals: U⁴⁺, As⁵⁺, Cd²⁺, Cr⁺², Cu²⁺, Ni²⁺, Pb²⁺, Zn²⁺, and V⁵⁺ in three different phosphate rocks from mines in Jordan. The mean values of uranium in the samples investigated were 98 ± 6 mgkg⁻¹, 92 ± 3 mgkg⁻¹, 215 ± 6 mgkg⁻¹, and 159 ± 13 mgkg⁻¹, respectively. The sequential extraction results obtained showed that most of the U⁴⁺ in these samples was strongly bound with 87%, 93%, 97%, and 93% of the total content, respectively, remaining in the samples after the sequential extraction steps were performed. Hence, 13%–7% and 3%–7%, respectively, of the U⁴⁺ is distributed in the most labile form, indicating that the majority of the U⁴⁺ in these samples was highly incorporated within the apatite present in the samples. The aforementioned was in agreement with the XRD and SEM-EDX results obtained. The apparent mobility of U⁴⁺, As⁵⁺, Cd²⁺, Cr⁺², Cu²⁺, Ni²⁺, Pb²⁺, Zn²⁺, and V⁵⁺ (using all six extraction steps) from the Al-Abied and Al-Hasa samples was as follows: As⁵⁺ (30.17%)> Cu²⁺ (6.55%)> Zn²⁺(4.34%)> Cd²⁺ (3.84%) Cr⁺² (3.66%)> Pb²⁺ (2.57%)> V⁵⁺ (53%)> Ni²⁺ (1.71%)> U⁴⁺ (0.99%). The mobility of As⁵⁺, Cd²⁺, Cu²⁺, Cr⁺², Ni²⁺, Pb²⁺, U⁴⁺, Zn²⁺, and V⁵⁺ (using all six extraction steps) from Eshidiya samples was as follows: As⁵⁺ (17.32%)> Cr⁺² (4.84%)> Zn²⁺ (4.25%)> Pb²⁺ (4.19%)> Cu²⁺ (3.49%)> V⁵⁺ (1.42%)> Cd²⁺ (0.78) U⁴⁺ (0.09%)> Ni²⁺ (0%).

Keywords:

• Trace metals
• mobility
• bioavailability
• phosphate rock
• partitioning
• Jordan

Acknowledgments

Dr. Al-Hwaiti gratefully acknowledges the Australian government for awarding him an Endeavour Executive Award to conduct research in the School of Applied Sciences, RMIT University, Melbourne. The authors would also like to thank R. Ibrahim, M. Tagreed, A, Mohammad, and Q. Raed of the Jordan Phosphate Mines for collection and preparation of samples. The authors are also grateful to Fiona Charalambous and Rahul Ram for their technical assistance. Thanks also go to two anonymous journal reviewers.