The formation of unsaturated zones within cemented paste backfill mixtures—effects on the release of copper, nickel, and zinc

Abstract

Flooding of cemented paste backfill (CPB) filled mine workings is, commonly, a slow process and could lead to the formation of unsaturated zones within the CPB fillings. This facilitates the oxidation of sulfide minerals and thereby increases the risk of trace metal leaching. Pyrrhotitic tailings from a gold mine (cyanidation tailing (CT)), containing elevated concentrations of nickel (Ni), copper (Cu), and zinc (Zn), were mixed with cement and/or fly ash (1–3 wt%) to form CT-CPB mixtures. Pyrrhotite oxidation progressed more extensively during unsaturated conditions, where acidity resulted in dissolution of the Ni, Cu, and Zn associated with amorphous Fe precipitates and/or cementitious phases. The establishment of acidic, unsaturated conditions in CT-CBP:s with low fractions (1 wt%) of binders increased the Cu release (to be higher than that from CT), owing to the dissolution of Cu-associated amorphous Fe precipitates. In CT-CPB:s with relatively high proportions of binder, acidity from pyrrhotite oxidation was buffered to a greater extent. At this stage, Zn leaching increased due the occurrence of fly ash-specific Zn species soluble in alkaline conditions. Irrespective of binder proportion and water saturation level, the Ni and Zn release were lower, compared to that in CT. Fractions of Ni, Zn, and Cu associated with acid-soluble phases or amorphous Fe precipitates, susceptible to remobilization under acidic conditions, increased in tandem with binder fractions. Pyrrhotite oxidation occurred irrespective of the water saturation level in the CPB mixtures. That, in turn, poses an environmental risk, whereas a substantial proportion of Ni, Cu, and Zn was associated with acid-soluble phases.

Constitutive Modeling of Cemented Tailings Backfill With Different Saturation States Based on Particle Swarm Optimization and Support Vector Machine

“…Besides, CTB may have different water saturation states due to the effect of groundwater [25][26][27]. The saturation states may significantly affect the compressive behavior of CTB.…”

Understanding the Opportunities, Barriers, and Enablers for the Commercialization and Transfer of Technologies for Mine Waste Valorization: A Case Study of Coal Processing Wastes in South Africa

“…Mining and primary ore processing operations produce large volumes of waste. These are normally disposed of in surface waste deposits such as tailings dams and heaps or backfilled into disused workings leading to the risk of environmental pollution [15][16][17][18][19][20][21]. Of particular concern in the case of wastes generated from sulfide-bearing hard rock ores and coal is the formation of acid rock drainage on exposure to air and water [22][23][24].…”

“…The coarse material (>1 mm) is called discards, while the fine material presents as slurry and is traditionally disposed of as tailings.). While current disposal practices, such as co-disposal and waste compaction, aim to minimize ARD generation by limiting air and water ingress [16,19,28], and advances in cementing technology are being made [29,30], they have yet to be proven effective in eliminating the generation of polluting discharges in the long-term, and continual monitoring will thus be required [15,18,31]. Furthermore, future disturbances by artisanal miners or land developers, for instance, could expose sulfidic minerals and thus increase the risk of ARD generation.…”