Geochemical behavior and environmental risks related to the use of abandoned base-metal tailings as construction material in the upper-Moulouya district, Morocco

In some developing countries, base-metal residues that were abandoned in tailing ponds or impoundments are increasingly used as construction material without any control, engineering basis, or environmental concern. This uncontrolled reuse of mine tailings may constitute a new form of pollution risks for humans and ecosystems through metal leaching. Therefore, the aim of the current study is to assess mine drainage, metal mobility, and geochemical behavior of two abandoned mine tailings commonly used in the upper-Moulouya region (eastern Morocco) as fine aggregates for mortar preparation. Their detailed physical, chemical, and mineralogical properties were subsequently evaluated in the context of developing appropriate alternative reuses to replace their conventional disposal and limit their weathering exposure. The obtained results showed that both tailings contain relatively high quantities of residual metals and metalloids with lead (ranging between 3610 and 5940 mg/kg) being the major pollutant. However, the mineralogical investigations revealed the presence of abundant neutralizing minerals and low sulfide content which influence mine drainage geochemistry and subsequently lower metals mobility. In fact, leachate analyses from weathering cell kinetic tests showed neutral conditions and low sulfide oxidation rates. According to these results, the tailings used as construction material in the upper-Moulouya region have very low generating potential of contaminated effluents and their reuse as aggregates may constitute a sustainable alternative method for efficient tailing management.

[Impact of polymetallic mine (Zn, Pb, Cu) residues on surface water, sediments and soils at the vicinity (Marrakech, Morocco)]

Metal sulphide tailings present a potential risk for the environment because of their natural oxidability which leads to the production of acid mine drainage. The prospected site close to Marrakech includes zinc, lead and copper sulphide deposits. This site is located in an agricultural area near the Tensift River which is used for irrigation. In addition to the tailing leachates, underground mine waters are also discharged into the river. This represents a potential risk for the environment and human health. The aim of this study was to assess the tailings impact on surface water, sediments and soil qualities. Chemical analysis of surface water and sediments collected downstream of the mine revealed that, water and sediments present high concentrations of major ions and heavy metals. The analysis also revealed spatial as well as temporal changes in the chemical properties of the studied water and sediments. These changes are attributed to the rising phenomena. The soil near the mine presents high content of sulphate. Its Zn, Pb, Cu and Fe contents are respectively 38, 15, 11 and 1.6 times higher than non contaminated soils located far away from the site. The soil irrigated with underground mine waters shows concentrations of SO4(2-), Cu, Zn, Fe, Cd and Pb which are respectively 4, 10, 28, 2, 9 and 12 times higher than soils which are not irrigated with this mine water. This study also showed that there has been a change in the physicochemical characteristics of water and sediments in the sampling points downstream of the mine before its closure and after its activity renewal.

[Impact of mining wastes on the physicochemical and biological characteristics of groundwater in a mining area in Marrakech (Morocco)]

Metal sulphide tailings represent a potential risk basically for the environment and particularly for water resources, because of their natural oxidisability which leads to the production of acid/neutral mine drainage. The prospected site close to Marrakech includes zinc, lead and copper sulphide deposits. This site is located in an agricultural area where ground water is used both for irrigation and drinking. Eco-toxicological investigations have been undertaken in order to asses the tailings impact on water quality in nearby wells. These investigations include physico-chemical characterization of the groundwaters as well as faunistic population determination. As compared to standard wells, waters from the wells located downstream of the mining site, have high electrical conductivities and high major ions contents, which can reach: 755 mg l(-1) in SO4(2-), 1670 mg l(-1) in Ca2+, 528 mg l(-1) in Mg2+, 2289 mg I(-1) in Na+ and 14981 mg l(-1) in Cl-. The fauna distribution analysis carried out around the studied wells shows qualitative and quantitative differences according to the flow gradient of the groundwaters. Areas located upstream of the mine tailings site are richer in stygobite species (Type and quantity) than those located downstream or close to it. It is likely that these biological differences are due to water quality alteration induced by the mining activity.

[Impact of acid mining drainage on the quality of superficial waters and sediments in the Marrakesh region, Morocco]

The aim of the present study is the evaluation of the effects of the acid drainage of three abandoned mining sites: SB-Othmane, Kettara and Draâ-sfar, on water and sediment quality of the Tensift River and its two temporary tributaries, the Kettara and El-Coudia Oueds. These mining sites located near Marrakesh contain mining residues abandoned for ten to twenty years. They are presently in an agricultural region of the Haouz district. In each site, these uncontrolled mining residues present a high level of metallic sulphide and generate, during rainy periods, leaching products which have physical and chemical characteristics of acid mine drainage (AMD). These percolates display an acidic pH ranging from 2.5 to 5.2, a high electric conductivity, large amounts of sulphate and heavy metals, especially under dissolved form (e.g. Cd: 17.34 mg l(-1); Fe: 1734 mg l(-1); Zn: 3935 mg l(-1)). Except for Pb, the free ionic form is the most abundant metallic form, as showed by calculations using the speciation GEOCHEM program. The analysis of water and sediments of the surrounding superficial aquatic ecosystems shows a modification of water chemical facies and an enrichment in heavy metals, mainly under the solid phase for Fe, Pb, Cu, Co, Cr and Ni, and under dissolved fraction for Cd and Zn. The dissolved fraction of these metals is dominated by the free ionic form, considered as available for organisms. Furthermore, sediments contain important quantities of heavy metals (Pb: 1450 microg g(-1), Zn: 1562 microg g(-1)) with an available fraction which is higher than 40% for the Cd and Zn. The abundance of trace elements (free ionic and available forms) in water and sediment presents a durable risk of their transfer to food chains.