Sustainable nexus for treating acid mine drainage: How does bio-alkali matrix impact acidity neutralization and heavy metal removal?

Acid mine drainage (AMD), characterized by high acidity and elevated concentrations of heavy metals, poses a persistent threat to ecological systems. Conventional neutralizers (NaOH, Na 2 CO 3 , Ca(OH) 2 ) raise pH effectively but generate large sludge volumes and incur high operating costs. Here, three urease-positive microbial consortia, enriched from soil and municipal activated sludge, were cultivated with urea to produce bio-alkali matrices (BAM-A/B/C, final pH 9.3). Abundant –CONH 2 , –NH 2 , –OH, and –COOH groups capable of chelating metal ions were found in BAM, suggesting alkaline buffering is complemented by ligand-mediated metal sequestration. When each BAM was mixed with AMD at a 3:10 volume ratio, the effluent pH stabilized at 7 and removal efficiencies reached ~100% for Al, Fe, Cr, Cd; > 90% for As, V, Co, Ni; 79 – 80% for Cu; and 60 – 62% for Mn. Geochemical analysis identified Fe/Al hydroxysulfates and organo-metal complexes as dominant precipitates. A full cost comparison showed BAM-A lowered treatment expenses to 35.5 RMB per m 3 , which is 12% below NaOH and 26% below Ca(OH) 2 , while reducing sludge generation. Coupling BAM with sulfate-reducing bacterial systems is advisable to enhance Mn and SO 4 2- removal. Overall, BAM provides an economical and environmentally sustainable alternative for AMD neutralization by uniting alkaline buffering with organic complexation. • BAM is fast and easy to produce, offers sustainable AMD treatment. • BAM neutralizes AMD acidity and removes heavy metals effectively. • Diverse organic compounds in BAM promote metal precipitation. • Economic analysis proves BAM's cost-effectiveness vs. commercial alkalies.