Chemical clogging of granular media under acidic groundwater conditions

Abstract

Generation of acidic groundwater attributed to pyrite oxidation in low-lying acid sulfate soil causes substantial damage to the soil-water environment and civil infrastructure. The installation of Permeable Reactive Barrier (PRB) is a frontier technology in the field of acid neutralisation and for removing toxic heavy metal cations, e.g. soluble Fe and Al. This study aims to assess the potential of limestone (calcite) aggregates as the PRB's main reactive material in low-lying pyritic land. During long-term laboratory column experiments, a significant capacity of limestone for removing the contaminant chemical species was observed. Nevertheless, the formation of secondary mineral precipitates upon geochemical reactivity within the granular media in the PRB caused armouring and chemical clogging that diminished the rate of reactivity, i.e. the treatment capacity of calcite aggregates, mainly at the entrance zone of the porous media. Flow properties were altered due to blockage of pores; for instance, hydraulic conductivity was reduced by 25% at the inlet zone. Non-homogeneous clogging towards the outlet was analysed, and the time-dependent effect on longevity of a limestone column was studied and quantified.

Spectroscopic and Modeling Investigation of Sorption of Pb(II) to ZSM-5 Zeolites

“…The typical pH of groundwater is in the range of 6–8.5, depending on the surrounding soil and rock types. Acidic groundwater also commonly exists in acidic mining discharge areas and in natural groundwater systems due to, for example, pyrite oxidation in acid sulfate soils. , Considering the wide range of groundwater pH, the experiments were carried out in increments of 1 pH unit, between pH 2 and 10, with a solid:liquid ratio of 1 g/L. The initial concentrations of Pb 2+ were 1, 5, 10, 20, 40, and 100 mg/L to determine the adsorption isotherm for ZSM-5.…”

Biogeochemical Clogging of Permeable Reactive Barriers in Acid-Sulfate Soil Floodplain

“…The large amount of CaCO3 (97%) indicates its obvious potential for neutralising acidic influent. The void ratio of limestone aggregates received from the plant was 0.57 and consisted of uniformly graded gravel-sized particles (GP) (ASTM D 2487(ASTM, 2000; Indraratna et al 2019).…”

“…Four horizontal acrylic columns (length = 65 cm, internal diameter = 5 cm) filled with limestone aggregates (Figure 1) were used to examine horizontal flow that mimics the motion of groundwater along transects parallel to the width and orthogonal to the length of a field PRB. The preparation of these columns and reactive material, which had been crushed and sieved to obtain uniform 4-5 mm sized particles, followed Indraratna et al (2019), albeit with some modifications to introduce acidophilic bacteria into the column.…”