Table 1.
Lixiviants and extraction conditions used for the determination of solid-phase partitioning of Fe, Cu, Pb, Zn and As from the ASGM-impacted and ‘control’ soil samples.
| Step | Extractant | pH | Liquid-to-solid ratio (mL/g) | Temperature (°C) | Duration (h) | Mixing speed (rpm) | Extracted phase |
|---|---|---|---|---|---|---|---|
| 1 | 1 M MgCl2 | 7 | 20/1 | 25 | 1 | 120 | Weakly adsorbed |
| 2 | 1 M NaH2PO4 | 5 | 20/1 | 25 | 1 | 120 | Strongly adsorbed |
| 3 | 1 M CH3COONa | 5 | 20/1 | 25 | 5 | 120 | Weak acid soluble |
| 4 | 0.04 M NH2OH·HCl in 25% acetic acid | – | 20/1 | 80 | 5 | 120 | Reducible |
| 5 | 0.04 M NH2OH·HCl in 25% acetic acid; 30% H2O2; 0.02 M HNO3 | – | 36/1 | 80 | 5 | 120 | Oxidisable |
| 6 | Calculated (i.e., Total of each element (XRF) – Sum of each element extracted (Steps 1 to 5) | Residual | |||||
∗Note: “–” means “not measured”.