Keeling, S.M. (2002) The role of phytoextraction in mine waste management. In: Green Processing 2002. pp. 139-146. From: International Conference on the Sustainable Processing of Minerals 2002, 29-31 May 2002, Cairns, QLD, Australia.

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Abstract

Botanical exploration has identified many plant species that naturally accumulate very high concentrations of elements, particularly heavy metals. The enormous potential applications of some of these species to remove metals from soil (phytoextraction) are slowly being realised. The discovery of hyperaccumulation has resulted in considerable research into applications for removing contaminants {phytoremediation) or more importantly, in the context of this discussion, for commercially 'farming' metals (phytomining) from metal-bearing soils.

Currently published phytoextraction models estimate Ni yields using Berkheya coddii (a South African nickclophyte) are approximately SUS 750 ha-1, excluding the cost of processing. Research indicates that B. coddii will also accumulate significant amounts of Co, resulting in a considerable increase in the value of the crop. Modification of the substrate by acidification, fertilisation and/or chelation indicate fruitful avenues for improving this yield by increasing the extractability of the target element, elevating biomass production rates and/or rendering other contained heavy metals extractable.

Plant uptake of more insoluble elements, such as Au, may be induced in many plant species using chemical compounds. These chelates applied to the soil, form soluble complexes with poorly soluble metals forcing them into the soil solution. Plants may then accumulate these metal complexes through transpiration. Research has achieved foliar Au concentrations of 78 mg kg⁻1 in Iberis intermedia, 56 mg kg⁻1 in Brassica juncea and 9 mg kg⁻1 in B. coddii (on a dry weight basis). Therefore in theory B. coddii could phytomine a soil containing modest concentrations or Ni, Co and Au to yield ll6 kg Ni, 36 kg Co and over 6 oz Au ha⁻1 at a current value or $US 4000. Root crops have also shown promise in chelate assisted Au accumulation (cg 6.8 mg kga1 in Beta vulgaris and 118.5 mg kg⁻1 in Raphanus sativus).

Phytoextraction, in its varied applications, is rapidly coming of age as a technology having considerable potential for application in environmental science and the minerals industry. Phytotechnology employs unique plant biochemical behaviours in the rhizosphere, driven by the sun's energy, to seek out and concentrate low levels of' heavy metals at very low cost.

Item ID:	14647
Item Type:	Conference Item (Research - E1)
ISBN:	978-1-875776-92-4
Date Deposited:	18 Oct 2017 23:06
FoR Codes:	04 EARTH SCIENCES > 0402 Geochemistry > 040202 Inorganic Geochemistry @ 100%
SEO Codes:	96 ENVIRONMENT > 9612 Rehabilitation of Degraded Environments > 961205 Rehabilitation of Degraded Mining Environments @ 100%
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