The effect of ferrous ions on hydraulic conductivity in fine tailings

The clogging of drainage facilities, which reduces the permeability coefficient, raises the phreatic line, and increases the possibility of seepage damage, seriously impacts the safety of tailings dams. The core cause of clogging is the oxidation of active minerals or ions and the formation of gelatinous materials. These materials, the most typical of which are active iron minerals (such as pyrite or ferrous ions), are adsorbed in the percolation passage to block the flow of liquid. This paper aims to study the effect of ferrous ions on the hydraulic conductivity of fine tailings. First, we introduce a new apparatus based on the column experiment to examine the permeation characteristics of fine tailings. Second, a systematic experimental study was conducted to obtain the effect of ferrous ion content, nonwoven geotextile layer number, and specimen height (reflecting the length of the seepage path) on the tailings permeability ratio using this apparatus. Third, scanning electron microscopy (SEM) was performed on selected geotextile samples that underwent filtration to assess the clogging mechanism. The results show that the ferrous ions were oxidized to form the low solubility iron(III) oxide-hydroxide (Fe(OH)3), which was deposited or adsorbed in the percolation channel and caused chemical clogging. Meanwhile, in the case of more geotextile layers or slower seepage rates, the blockage of the fine tailings formed faster in the penetration experiment. According to the results of the SEM, there were glue coverings on the fiber surface, and ultrafine tailings particles (−10 μm) were adsorbed, adhered and deposited on it and formed a chemical-physical clogging. •Clogging formation is more sensitive to ferrous ions content in the tailings sample.•Geotextile thickness (or number of layers) has a significant impact on the formation of clogging.•The ultrafine particles (−10 μm) are more easily adsorbed, banded, and even encapsulated by colloidal compounds.•Clogging formation seems to be dependent on the hydraulic environment.