Reclamation of red mud (bauxite residues) using alkaline-tolerant grasses with organic amendments

Distichlis spicata var. stricta (desert saltgrass), Sporobolus airoides (alkali sacaton), Agropyron smithii (western wheatgrass), and A. elongatum (tall wheatgrass), alkaline-tolerant grasses of the western United States, were tested as species to colonize and cover red mud (bauxite residue) with minimum use of soil amendments. A gradient in red mud texture at a residue impoundment (coarse at edge to fine in the center) located in Mobile, Ala., was correlated with soil pH that ranged from 9.15 (coarse) to 11.9 (fine). Saturation-extract Na concentrations ranged from 394 to 4,990 mg/L and Al concentrations from 4.3 to 1,004 mg/L. Exchangeable Na percentage ranged from 52.6 to 91.1. Without amelioration red mud impoundments lacking subsurface drainage remain unvegetated indefinitely. Sewage sludge additions to red mud (2 cm on surface, or 1:2 by volume) produced significantly greater growth compared with red mud controls with D. spicata var. stricta, A. elongatum, and S. airoides in greenhouse pot experiments. Other organic amendments (wheat straw, paper pulp waste, glucose, and pine needles) and complete nutrient additions failed to produce a consistent response. Sewage sludge caused similar growth increases with D. spicata var. stricta in field experiments on drained red mud lakes. Sewage sludge may increase growth via several mechanisms: (i) lowering red mud pH, (ii) adding macro- and micronutrients, (iii) increasing nutrient availability through chelation, and (iv) lowering potential Al toxicity.

Duke Scholars

Author Curtis J. Richardson Environmental Sciences and Policy