Metal transport and remobilisation in a basin affected by acid mine drainage: the role of ochreous amorphous precipitates

Abstract

Metal-polluted mine waters represent a major threat to the quality of waters and sediments in a downstream basin. At the confluence between acidic mine waters and the unpolluted waters of the Gromolo Torrent (Liguria, North-West Italy), the massive formation of an ochreous amorphous precipitate takes place. This precipitate forms a soft blanket that covers the torrent bed and can be observed down to its mouth in the sea. The aim of this work is to evaluate the dispersion of metals in the Gromolo Torrent basin from the abandoned Cu-Fe sulphide mine of Libiola to the Ligurian Sea and to assess the metal remobilisation from the amorphous precipitates. The mineralogy of the superficial sediments collected in the torrent bed and the concentrations of different elements of environmental concern (Cu, Zn, Cd, Co, Cr, Mn, Ni, Pb, As, and Sb) were therefore analysed. The results showed that the precipitates contain high concentration of Fe, Al, Cu, and Zn, significantly modifying the bulk chemistry of the Gromolo Torrent sediments. In order to evaluate the possible remobilisation of ecotoxic elements from the amorphous precipitates, bulk leaching tests were performed with both deionised and seawater. Bulk leaching tests with deionised water mobilised primarily high Pb amounts, but also relatively high concentrations of Fe, Al, Cu, and Zn are released in the leachate. In seawater tests, Fe, Al, Cu, and Zn were released in smaller amounts, while other elements like Mn, Cd, Co, and Ni increased in the released fraction. Pb was still strongly released as in deionised water experiments. The results show that the interaction of precipitates and seawater can remobilise high concentrations of metals, thus affecting the surrounding environment.

Sediment distribution on the continental shelf in relation to stream inputs and contamination: hydrodynamic, chemical, mineralogical, and sedimentological characteristics (Ligurian Sea, Italy)

“…In fact, it is well known that these metals are typical tracers of sediments deriving from such rocks (Dey et al 2018 ; Salmanpour et al 2017 ). From this, it is possible to deduce that the distribution of Mg, Cr, and Ni in the superficial bottom sediments is mainly controlled by the input of the Gromolo Stream due to the geology of its catchment basin and the Libiola mine waters that it receives and brings to the sea (Consani et al, 2017 ). The origin of these elements is mainly geological; therefore, even if their concentration exceeded the threshold set by the Italian Law (Italian Ministerial Decree 56/2009) as reported in Table 4 , they did not represent a “real” contamination.…”

Моделирование Осаждения И Трансформации Гидрогенных Минеральных Фаз Кислых Шахтных Вод

“…Самопроизвольно осаждаясь, гидроксисульфаты Fe, обладая высокой удельной площадью поверхности и высокой реакционной способностью, могут сорбировать и/или соосаждать такие металлы, как As, Pb, Cr, Cu, Zn, Mn, Cd, Co, Ni и др. [5].…”

“…При смешивании кислых шахтных и нейтральных природных вод растворимость металлов значительно снижается, происходит осаждение железа и алюминия в виде аморфного охристого осадка, который покрывает дно и берега принимающих водоемов на многие километры вниз по течению [3,5]. Образующиеся частицы с гетерогенным составом и низкой кристалличностью удерживают за счет адсорбции и/или соосаждения многие токсичные элементы, присутствующие в шахтных водах [5]. Эти нано-и микрочастицы могут образовывать крупные агрегаты и осаждаться в русле рек, или мигрировать на большие расстояния в виде взвеси.…”

“…Эти нано-и микрочастицы могут образовывать крупные агрегаты и осаждаться в русле рек, или мигрировать на большие расстояния в виде взвеси. Изменения физико-химических параметров, таких как Eh, рН, могут приводить к растворению минеральных фаз, высвобождению токсичных элементов и их рассеиванию в водной среде [5].…”

Characterization and Treatment of Mine Drainage

“…Metal remobilization from ochreous amorphous precipitates was evaluated in the Gromolo Torrent basin, an abandoned Cu-Fe sulfide mine of Libiola to the Ligurian Sea (Consani et al, 2017).…”