Performance of polymer-enhanced bentonite–sand mixture for covering arsenic-rich gold mine tailings for up to 4 years

Abstract

Experiments conducted over a 4-year period, on a polymer enhanced bentonite-sand mixture (PEBSM) used as cover for gold mine tailings are reported. The effect on PEBSM hydraulic conductivity (k) of subgrade porewater chemistry, subgrade water content, and confining stress are investigated. Results show that the reduction in the mole fraction of bound Na + (ESP) and corresponding increase in k of PEBSM with time was highly dependent on the ionic strength of the subgrade porewater. When the PEBSM was in direct contact with gold mine tailings with porewater having an ionic strength of 145 mM, ESP decreased from 59% to 2% and k increased from 4x10 -11 to 6.9x10 -9 m/s. The ESP and k values of PEBSM over tailings with 11 mM porewater were 21% and 6.9x10 -11 m/s. A 0.15-m-thick foundation layer between tailings and PEBSM layer significantly lowered the reduction in ESP and increase in k with time as did a reduction in the subgrade water content. There was no effect of changing confining stress from 15 to 7.5 kPa on k values of PEBSM. The PEBSM layer acted as a good barrier to the migration of arsenic from tailings upward towards cover soil above PEBSM layer.

Review of Research on Physical and Mechanical Properties and Engineering Application of Metal Tailings

“…Subgrade filling has certain requirements for the selection of filling material [57]. The selection of tailing sand should consider both the influence of radioactivity and the influence on the water environment.…”

Studies on Hydration Swelling and Bound Water Type of Sodium- and Polymer-Modified Calcium Bentonite

“…The polymer modification mechanism is that the modifier polymers with special functional groups enter the montmorillonite layer and form layered structures such as intercalation and exfoliation. Many researchers [31][32][33] have conducted experimental studies on polymer-modified bentonite for antiseepage performance, and the latest experimental results have been applied to vertical cutoff walls for antiseepage performance [34]. The mechanism for enhancing antiseepage performance is as follows: (1) The intercalation of polymer into the clay mineral layer enhances the swelling of bentonite caused by chemical osmotic pressure.…”

The Potential of Bentonite and Chitosan Mixtures as Clay Liner Base Material

“…Some of the benefits of this material include almost no difference in water retention during the drying and wetting processes, a large ability to expand so that it has very low permeability, and no cracks when conditions are dry [3]. Field investigation reveals that the PEBSM layer prevented arsenic migration from tailings to the cover soil above it [4].…”