Properties of humic acids from copper tailings 20 years after reclamation

Abstract

Part of Cu post flotation tailings of Serbia ZiJin Bor Copper, Serbia, was reclaimed by restoration of top soil with arable soils, and revegetation in 1991. Humic acids isolated from these Technosols were investigated to find out if their properties underwent any changes since reclamation. Two groups of control samples were used. Elemental composition (CHNS analysis) falls within the range of average soil humic acids. Humic acids belong to the type B pointing out to its lower humification degree (UV–Vis). Relative abundances of functional groups are ranged as follows: polysaccharide C ³ aromatic C > carboxyl C > OH group > aliphatic C. Aromaticity indexes are low, 1.88–3.25 (ATR-FTIR). Basic units at pH 10 are in the 11.7–26.8 nm range. Pro­nounced reaggregation (1462‑–5218 nm) at pH 3 points out to less expressed humic acid sol stability, as well as to increase in aromatic condensation degree (dynamic light scattering). No significant changes have occurred in technosol humic acids since the recultivation, confirming stability of their properties over time (PCA). Never­theless, humic acids from very strongly acidic Technosols show higher humify­cation degree possibly originating from arable soils used in reclamation, but more likely from low soil pH and low litter input, results of unsuccessful reclamation.