Revegetation of alumina refinery wastes. 1. Properties and amelioration of the materials

Abstract

Excess soluble salts (EC 30 to 48 mScm-1), high alkalinity (pH 9.2 to 11 .0) and potentially toxic levels of sodium (ESP 49 to 88 per cent) were characteristic of fly ash and bauxite wastes ('red sand' and 'red mud') from the Gladstone alumina refinery. In red sand, N and P levels were extremely low and Zn and Mn marginal; extremely low levels of N and P and a marginal amount of Zn were measured in the red mud. Fly ash was characterized by a potentially toxic level of B and deficiency levels of N and Zn. The physical limitations of low water holding capacity of red sand and the susceptibility of fly ash to wind erosion were reduced by mixing the wastes. Excess soluble salts in fly ash-red sand mixtures were effectively removed by leaching without an accompanying decrease in the saturated hydraulic conductivities of the solids. Following the reduction in salinity, the pH values of the wastes remained high (8.4 to 9.6). Incubation of the ash and sand with NH4NO3, superphosphate, FeSO4.7H2O, FeS2 and S for up to ten weeks demonstrated that FeSO4.7H20 was the most effective acidulant in the short term. Reduction of the excessive exchangeable sodium percentages in ash (49 per cent) and sand (88 per cent) to levels tolerable to plant growth was achieved by leaching and acidification.