Evaluation of aggregate formation, stability and pore characteristics of bauxite residue following polymer materials addition.

Bauxite residue has poor physical conditions, which hinders plant growth and causes potential environmental risks. Polymer materials have broad potential applications for holding water and improving soil aggregation. However, no attempt has been made to assess the effects of polymers on physical structure of bauxite residue. The purpose of this study was to evaluate the effects of polyacrylamide (BP), humic acid (BH), starch-acrylamide polymer (BSA) and humic acid-acrylamide polymer (BHA) on aggregate formation, stability, and pore characteristics in bauxite residue by 60-day pot experiment. Results demonstrated that 0.2% polymer addition increased the proportion of >0.25 mm mechanical-stable aggregates. Under wet sieving, BP and BHA treatments increased the values of mean weight diameter (WMWD) from 0.36 mm to 0.67 mm and 0.68 mm, respectively, which may result in the increase of the percentage of organic functional groups including OCO and CC. Laser diffraction analysis and the visualized 3D surface map revealed that >0.25 mm residue aggregate was more difficult to disintegrate following BHA treatment during 180-min hydraulic circulation. BP and BH treatments elevated <0.5 µm pore size volumes, whilst BHA treatment increased >5 µm pore size volumes and improved the porosity of bauxite residue. Polymer applications indicated that compared with polyacrylamide or humic acid, humic acid-acrylamide polymer could be regarded as an effective ameliorant due to its positive effects on both aggregate stability and pore characteristics. These findings were helpful for understanding the application potential of natural-synthetic polymers on physical conditions of bauxite residue prior to ecological reconstruction on the disposal areas.