Effects on organic matter on heavy metal fractionations of tailings: a case study of Akara Gold Mine, Thailand

Abstract

The purpose of this study was to investigate metal fractionations of mine tailings (i.e., Co, Cr, Cu, Mn, Ni, Pb and Zn) and study of metal leaching from mixtures of tailing and humic acid in different incubation periods and various organic matter ratios. Ten tailing samples were taken from tailings storage facilities of Akara gold mine in Phichit province. Samples were determined using the three-step modified BCR sequential extraction (i.e., BCR1, BCR2 and BCR3) and the additional step of strong acid digestion or aqua regia for residual fraction and analyzed all fractions by Inductively Couple Plasma-Optical Emission Spectrometer (ICP-OES) and reported their concentrations in the unit of mg/kg soil. Amount of metals in such tailings were showed in percentage of BCR1, derived from concentrations of each metal in BCR1 divided by those in all fractions, and were ranged in descending order as follows: Mn > Co > Ni > Cu > Zn > Pb > Cr, that were 32.29% (622.91 mg/kg soil), 8.88% (2.08 mg/kg soil), 8.20% (7.68 mg/kg soil), 8.11% (7.68 mg/kg soil), 6.80% (16.10 mg/kg soil), 3.85% (3.74 mg/kg soil) and 0.45% (0.55 mg/kg soil), respectively. Percentage of metal in BCR 2 were ranged in descending order as follows: Co > Mn > Pb > Ni > Zn > Cr > Cu , that were 51.90% (15.95 mg/kg soil), 40.82% (787.47 mg/kg soil), 34.91% (33.94 mg/kg soil), 26.40% (6.71 mg/kg soil), 22.62% (53.58 mg/kg soil), 13.27% (16.46 mg/kg soil) and12.33% (11.67 mg/kg soil), respectively. As a result, the mobility orders of these metals were Mn > Co > Pb > Ni > Zn > Cu > Cr. Tailings were mixed with humic acid with various ratios of organic matter (5%, 7% and 10%) and with different incubation periods (1, 7, 15 and 30 days) in order to determine the optimum condition of different organic amendment ratios and times on reduction of metal mobility. Soil tailings had a pH around 8.25 and humic acid were 74.59% organic matter. When samples were mixed into those ratios and then analyzed all results through SPSS Statistic program by using ONE-WAY ANOVA and post hoc test with LSD method (Fisher’s Least significant difference). The optimum condition of mixing were ten percentage of organic matter as compared to other treatments, which showed statistical significantly lower concentration of metals leached out (p<0.05). Semi-log linear regression analysis was then used to determine the relationship between times and ratios of organic matter with metal concentrations in each fraction. Metal concentrations of first two fraction were mainly focused on and found that amounts of Cu Zn and Pb were reduced in BCR1 and Cu Cr and Pb were reduced in BCR2 (R2>0.5). Moreover, the results showed that amounts of Cu and Pb in BCR 1 and Ni in BCR2 reduced with increasing time aging increased (R2>0.5).