Acid Mine Drainage at the Abandoned Kettara Mine (Morocco): 1. Environmental Characterization

Abstract

The Kettara site (Morocco) is an abandoned pyrrhotite ore mine in a semi-arid environment. The site contains more than 3 million tons of mine waste that have been deposited on the surface without concern for environmental issues. Tailings were stockpiled in a dyke and pond and in piles, over an area of about 16 ha, and have generated acid mine drainage (AMD) for more than 24 years. The mine waste and secondary precipitates from this mine were characterized using geochemical and mineralogical techniques. The Kettara wastes contain 1.6-14.5 wt% sulfur, mainly sulfide minerals (e.g., pyrrhotite, pyrite, chalcopyrite, galena, and sphalerite). The main gangue minerals were goethite, quartz, chlorite-serpentine, talc, muscovite, and albite. Carbonates occur at very low quantities (less than 1 wt%). The most abundant heavy metals were Cu, Zn, Cr, Pb, Co, As, Cd, and Ni. Acid-base accounting static test results showed that all the samples have low values of acid-neutralizing potential (NP) (0-9 kg CaCO3/t). The mine waste has high acid-producing potential (AP) (51-453 kg CaCO3/t). Abundant secondary mineralogy is present, consisting mainly of halotrichite, goethite, jarosite-hydroanion, hydroniumjarosite, starkeyite, gypsum, alunite, copiapite, butterite, and coquimbite. Hardpans, which can prevent water infiltration to fresh tailings beneath and thereby lessen the rate of sulfide reactivity, were observed during sampling of the fine tailings. Mineralogical analysis indicated that the cementitious phase of the hardpan is mainly goethite. The alteration observed in the tailings pond does not extend more than 5-15 cm.

Control of acid mine drainage from an abandoned mine in Morocco by using cement kiln dust and fly ash as amendments

“…The Iron, which could be associated with pyrrhotite and pyrite, is present in these solid tailings with relatively large amounts [46,48]. These High concentrations of some toxic metals contaminate soil, aquatic ecosystems, wildlife as well as human health [48].…”

“…Tailings were stockpiled in a main pond, but also in a dyke, and in smaller piles over an area of approximately 16 ha. The abandoned Kettara Mine generates acidic leachates with a pH between 2.9 and 1.5 [46,48]. The acidification potential (AP) of that is between 51 and 453 Kg CaCO 3 /t while the net of neutralization potential (NNP) ranges from -453 to -22.5 Kg CaCO 3 /t [46].…”

“…This mine site remains hazardous. It generates a large AMD in the tailings park [46,48] and therefore requires control.Tailings samples from the Kettara mine (TK) are corresponding for unweathered coarse tailings. They were collected at a depth of 1 m from an exploratory trench which was excavated in the 15 m high dyke.…”

“…The abandoned Kettara Mine generates acidic leachates with a pH between 2.9 and 1.5 [46,48]. The acidification potential (AP) of that is between 51 and 453 Kg CaCO 3 /t while the net of neutralization potential (NNP) ranges from -453 to -22.5 Kg CaCO 3 /t [46]. The permeability test of samples has provided permeability between 4.9 10 -2 cm/s and 1.1 10 -1 cm/s, so these tailing are classified into the range of perfectly permeable materials [30].…”

“…The mine is currently one of several abandoned mine sites in Morocco producing AMD, that contaminates soils [45], and surface water and groundwater [46,47] (Figure 2c). More than 3 million tons of mine wastes deposited on the surface of the Kettara site without any concern for environmental consequences have generated significant AMD for more than 30 years.…”