Zinc forms in compost and red mud-amended bauxite residue sand
*Subscription may be required
Purpose: Re-vegetation is the preferred long-term practice for managing Alcoa's bauxite-processing residue storage areas. Residue sand is the primary growth medium for rehabilitation; however, it is largely nutrient deficient. Although addition of organic and inorganic amendments can provide short-term supply of plant-available nutrients, but quickly exhausted, thus long-term deficiencies are often observed. The rapid transformation of added zinc into non-available pools is predicted as the main factor limiting vegetation performance. Materials and methods: Two laboratory investigations were carried out to assess the effect of organic (composts) and inorganic (various types of red mud) amendments on Zn availability in residue sand. Three compost mixtures (piggery, biosolid and commercial compost), three rates of application (0, 10 and 50 t ha-1) were taken as organic amendments and incubated with residue sand for 30 days to examine the effects of compost on Zn availability. Seven column treatments were set up as: control residue sand, homogeneous mixtures of residue sand with 3% (w/w) and 8% (w/w) seawater-washed, carbonated or unaltered red mud with residue sand. Leaching with distilled water was carried out every 3 days by adding 1/6th pore volume and analysed for Zn availability and its distribution in various chemical pools. Results and discussion: Fractionation studies found that Zn availability decreased with incubation time and red mud amendments. Residue pH and organic C were the major factors controlling Zn availability and its distribution. Column studies showed limited Zn mobility in residue sand even after three pore volumes of drainage. Increased DTPA extractable Zn in surface layers of residue sand with and without red mud amendments after leaching was found and attributed to decrease in residue water-soluble alkalinity. Addition of commercial compost (50 t ha-1) increased DTPA Zn, decreased the alkalinity and increased C content in residue sand. The red mud amendments had contrasting effects on Zn that were related to pH of the materials. Addition of seawater-washed red mud increased DTPA Zn in residue sand whereas unaltered red mud decreased DTPA Zn. Conclusions: Plant available Zn extracted with 50 t ha-1 of commercial composts addition was well above deficient range, suggesting that they could be an effective Zn source for vegetation establishment. Zinc occurred predominantly in organically bound form in compost-amended sand and as carbonate-bound form in leached red mud-amended columns, but the longer term effects of these Zn forms on the release of Zn for plant growth remain unclear.
|Publication Type:||Journal Article|
|Murdoch Affiliation:||School of Environmental Science|
|Copyright:||© 2010 Springer-Verlag.|
|Item Control Page|