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Thallium phytoextraction and its economic significance: a thesis presented in partial fulfilment of the requirements for the degree of Master of Science at Massey University
(Massey University, 2000) LaCoste, Cher
Thallium is a volatile toxic metal which has many industrial uses. The sources of thallium include natural geochemical sources and by-products of industrial processes. One of the problems in assessing thallium pollution potential is the lack of an accurate method of quantification of this element. Flame atomic absorption spectrometry (FAAS) is a good method of analysis but only down to the 1.0 mg/kg (ppm) level. For lower concentrations, analytical techniques have been difficult and inaccurate. A newly described method using graphite furnace atomic absorption spectrometry (GFAAS) has been found useful for low T1 concentrations. A method was designed to detect low concentrations of thallium in plant and soil samples. The graphite furnace technique worked well for the data presented in this paper. However, samples of different origin could have more severe matrix effects such as high iron contents. Thallium has been found to be readily available for plant uptake. The extractability of thallium was significantly higher then other metals such as cadmium and zinc. This property is ideal when considering a possible phytoextraction operation. Two plant species were found to accumulate thallium to levels up to 411 mg/kg in Iberis intermedia and 504mg/kg in Biscutella laevigata. These high values indicate potential for phytoremediation and phytomining in areas of sufficient contamination. The properties of which make thallium an ideal candidate for phytoremediation also make the metal a high risk for biota. Experiments were also conducted to determine the partitioning and sequestration of thallium within plant organelles. This work was limited to the two hyperaccumulating species but future work could compare non-tolerant species. Evidence from this research might give a better understanding to the mechanism involved in plant uptake and storage of thallium. Agricultural crops used for human consumption or animal grazing may cause deleterious health effects. Thallium is extremely toxic, effecting the nervous system and impairing heart function at low levels. Higher concentrations will cause death. It is possible that some of the illness symptoms observed in humans may be derived from low levels of thallium in foodstuffs. Aside from a few economic mineral deposits, there is no information of a world-wide distribution of thallium, so health effects can not be accurately assessed. This thesis describes experiments carried out on common vegetable and their uptake of thallium to determine safe levels of this element within the soil. This information will also be useful to farmers growing crops on contaminated soil will advise them on which plants would uptake less thallium. Thallium has not been studied as extensively as many other heavy metals that are more common in the environment. Although the crustal abundance of thallium is low (0.49-0.7 mg/kg average range), the toxicity of this element is very high, and it is readily available for plant uptake. The toxic effects on animals and plants should be monitored closely.
The recovery of nickel from hyperaccumulator plant ash : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry at Massey University, Palmerston North, New Zealand
(Massey University, 2000) Kirk, Anthony Hans Peter
Nickel hyperaccumulator plants have the unusual ability to absorb nickel from the soil they grow in and incorporate it into their structure, to concentrations greater than 1% dry weight. This selective accumulation process occurs with the relevant exclusion of most other metals from the plant material. Combustion of this material then results in a nickel-rich ash (10-15%) of relatively high purity when compared to commercially mined ore (1-4% Ni). Much work has focused on the plants themselves, with suggestions of them being applied to the commercial extraction of nickel from soil, with yields up to 200 kg per hectare. However, little work has been undertaken on the recovery of nickel from the plant material. Given the refined nature of nickel hyperaccumulator ash and that any commercial enterprise is governed by economics, it was thought that a more specific nickel recovery process could be determined for the ash than simply smelting with nickel ore. Such a process should produce an end product of greater worth than smelted nickel. To this end nickel electrowinning and nickel salt crystallisation were investigated. Ashing of the plant material by open flame combustion was found to produce a bio- ore suitable for nickel solubilisation, with the energy produced by the process possibly being of economic benefit if applied to the generation of electricity. Leaching of the nickel from the ash was investigated using a variety of acids with sulfuric acid primarily used, owing to the common usage of a sulfate medium in both nickel electrowinning and crystallisation. A 96% solubilisation of the nickel from the ash was achieved using 4M H₂SO₄, with resulting extracts containing nickel at approximately 0.35 mol/l concentrations. The addition of nitric acid to aid in nickel leaching while successful, also solubilised greater quantities of impurities and caused complications in later processing. Electrowinning of nickel from an ash extract solution, once neutralised to pH values of 4-6, required the balancing of sulfate and nitrate concentrations. Excesses or indeed the absence of either, proved to inhibit metallic nickel electrodeposition, instead two different hydroxide products were observed. However, once balanced a metallic nickel deposit was produced with a current efficiency for the electrowinning period of 94%. From solutions containing a range of potassium and nickel sulfate concentrations it is found that the double salt K₂Ni(S0₄)₂.6H₂O will crystallise. The ash extract, being of hyperaccumulator origin, contains both Ni and K in high concentrations, with SO₄²- being added during the leaching process. It was found that double salt crystals formed without chemical aid even in a highly acidic solution, but with the addition of KOH and/or K₂SO₄ could be crystallised to the extent where as little as 1.5 g/l Ni remained in solution. The blue/green cubic crystals are easily recovered in good yield, corresponding to a 98% recovery of nickel from the ash extract. While no large market exists for the material at present, there are possibilities for its use and given a theoretical yield of 690 kg K₂Ni(SO₄)₂.6H₂O per hectare, there is potential for substantial monetary return.
The phytoextraction of gold and palladium from mine tailings : this thesis is presented in fulfilment of the requirements for the degree of Master of Philosophy
(Massey University, 2002) Walton, Dylan
The extraction of gold and palladium from a South African mine tailing (Klipfontein) and artificial substrate was examined. A variety of solutions were tested and extractants observed to dissolve large quantities of metal were subsequently used in trials investigating plant uptake of gold and palladium. Extraction by thiocyanate amended with an oxidising agent dissolved large amounts of gold and palladium from the test substrates. Various combinations of thiocyanate/Fe(III) and thiocyanate/H 2 O 2 were examined. Metal extraction in the thiocyanate/Fe(III) showed dependence on redox potential and acidity of the solution; this dependence was not observed in the thiocyanate/H 2 O 2 system where production of cyanide may be an important factor. The addition of iodide to thiocyanate/Fe(III) did not affect dissolution of metals. Thiourea was also tested. This chemical was shown to be a relatively poor extractant of gold and palladium, with and without an oxidant. Two plant species, Berkheya coddii and Brassica juncea, were investigated in plant trials. Initial experiments showed uptake of metals to be independent of plant species. Greatest metal uptake was achieved using cyanide as a chemical amendment, with nearly 500 ppm gold accumulation in B. juncea planted in artificial substrate and treated with 1 gL -1 KCN every day over 6 days. Nearly 13 ppm palladium had accumulated in these plants - the highest average concentration observed with any treatment. KCN also induced the largest metal uptake from Klipfontein substrate – nearly 1600 ppb gold and 7700 ppb palladium accumulation in B. coddii. As an exercise it was shown that the value of gold and palladium that would be recovered from a phytomining operation on Klipfontein substrate would be greater than the cost of cyanide added in such an operation. Plant uptake of gold and palladium from the mine tailing after treatment with thiocyanate plus an oxidant was poor. Gold and palladium uptake by B. coddii from artificial substrate after treatment with thiocyanate + H 2 O 2 was improved, with levels of accumulation similar to that of cyanide. Metal uptake by thiocyanate + Fe(III), however, remained poor. The conclusion of this thesis is that phytomining of gold and palladium offers large potential in both practical and research terms. The relative importance of the species thiocyanate, H 2 O 2 , and cyanide remain unknown in the thiocyanate/H 2 O 2 system and further research is needed to elucidate this behaviour.
The economic significance of the phytoextraction of nickel, cobalt and gold from metalliferous soils : a thesis in partial fulfilment of the requirements for the degree of Master of Science at Massey University
(Massey University, 2000) Keeling, Scott M
Phytoextraction of heavy metals is a relatively new technology that has potential applications for the remediation of many contaminated sites around the world. The technology has significant applications in the minerals industry for the treatment of low-grade ores and metalliferous mine waste. This study concerns the investigation of the potential to remove heavy metals, in particular nickel, cobalt and gold, from artificial and lateritic substrates. Four experiments comprise this study of the phytoextraction of nickel, cobalt and gold using both accumulator and non-accumulator species. Nickel and cobalt bioavailability was determined by ammonium acetate extraction for both artificial and laterite substrates. It was found that ammonium acetate extractability was predictive for nickel accumulation from a nickel-only artificial substrate. Cobalt bioavailability did not predict the accumulation response of either Alyssum bertolonii or Berkheya coddii grown of artificial substrates. The potential for phytoextraction of nickel and cobalt was investigated using the known nickel hyperaccumulators A. bertolonii and B. coddii, grown on artificially prepared substrates. The substrates were nickel-only (4 mg/kg to 1000 mg/kg), cobalt-only (4 mg/kg to 1000 mg/kg) and nickel-cobalt mixed (1:1 ratio, 4 mg/kg to 500 mg/kg) amendments of sulphates to commercial potting mix. Hyperaccumulation from nickel-only and cobalt-only substrates resulted in typical logarithmic metal uptake by both species. The cobalt-only substrates were phytotoxic to B. coddii above a concentration of 15-20 mg/kg. Phytotoxicity significantly reduced biomass production in B. coddii without effecting the bioaccumulation coefficient. No corresponding cobalt phytotoxicity was observed in A. bertolonii over the experimental range, although biomass production appears to favour substrate concentrations below 30 mg/kg. The bioavailability and hyperaccumulation of cobalt from the mixed nickel-cobalt substrates dramatically reduced the nickel accumulation potential of both species at substrate concentrations below 300 mg/kg. At higher substrate metal concentrations both species return to nickel dominant hyperaccumulation. Induced gold accumulation in B. coddii and Iberis intermedia was investigated using, sequential ammonium thiocyanate and ammonium thiosulphate chelation to, a 5 mg/kg gold artificial substrate. An attempt to determine gold bioavailability by ammonium thiocyanate and ammonium thiosulphate extraction was made on the substrate. It was found that neither chelator extraction could be correlated with plant accumulation induced by the same concentration of the reagent. Ammonium thiocyanate induction resulted in plant gold accumulation at or below the substrate concentration. Ammonium thiosulphate induced gold accumulation in I. Intermedia reached 48.8 mg/kg when treatment with a 1% solution. B. coddii accumulated 9.3 mg/kg gold for the same treatment. Five consignments of metalliferous lateritic materials from Western Australia were investigated. Three substrates originated from Project Murrin Murrin nickel and cobalt mine operated by Anaconda Nickel Ltd. and two substrates originated from Boddington Gold Mine operated by Worsley Alumina Ltd. Nickel and cobalt accumulation by A. bertolonii and B. coddii was found to be significantly lower than observed using artificial substrates. Nickel and cobalt bioavailability, determined by ammonium acetate extraction, failed to predict the accumulation responses from laterite substrates. This is attributed to elemental interference by, and possibly ammonium acetate chelation of, other mobile heavy metals in these substrates. A hypothesis deserved of further research. Hyperaccumulation of nickel was observed for both species on the Anaconda Nickel Ltd. SAP substrate only. Appreciable cobalt accumulation (≈90 mg/kg) was observed on the SAP substrate for both species and on the Boddington Gold Mine B5 substrate for B. coddii. Phytomining scenarios were determined for both species grown on the SAP substrate. A. bertolonii could produce 13 kg of nickel and 0.8 kg of cobalt per hectare with a value of US$ 163. B. coddii could produce 23.8 kg of nickel and 2.1 kg of cobalt per hectare at a value of US$ 319. These levels of production could be improved by fertilisation and/or substrate acidification. A preliminary investigation into induced gold accumulation from laterite substrates by I. Intermedia, A. longiflora, Brassica juncea and Limum usitatissimum was made using the acid biased chelator ammonium thiocyanate. It was found that an acidified amendment of ammonium thiocyanate greatly improved the phytoaccumulation of gold from the lateritic substrates. An amendment of 2M HC1 produced appreciable gold mobility and phytoaccumulation and indicates that gold solubility is the primary control on plant uptake. Analysis of various plant tissues indicated that Acacia longiflora stored significant gold in its roots compared to foliar components. All plant-substrate combinations indicated a trend towards increasing acidification and gold phytoaccumulation. No plant-substrate-treatment combination produced an economically viable phytomining scenario.
Biogeochemical studies in South East Asia by use of herbarium material : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry at Massey University
(Massey University, 1977) Wither, Ewan David
A biogeochemical survey of Indonesia was undertaken analyzing herbarium samples by atomic absorption. (Indonesia was chosen because it has been well surveyed botanically, but poorly surveyed geologically.) Background concentrations of copper, nickel and zinc were determined using various species, predominantly members of the families Flacourtiaceae and Violaceae. Rinorea bengalensis (wall) O.K. (Violac.) was discovered as a hyperaccumulator of nickel (Brooks et al., 1977) and this led to an in depth study of R. bengalensis and other species of the genus. From this study two areas of doubtful geology were predicted as containing ultrabasic rocks, R. javanica (B1.) O.K. was shown to be a hyperaccumulator of nickel and R. albersii Engl. was found to yield a very high cobalt/nickel concentration ratio. Three hyperaccumulators of nickel were discovered after analysis of a selection of herbarium samples collected on Obi Island by Dr. E. de Vogel. (They were: Myristica laurifolia Spruce ex DC var. bifurcata (Myrist.); Planchonella oxyedra Dubard (Sapotac.); Trichcspermum kjellbergii Burret (Tiliac.).) Ambon Island was predicted as consisting of ultrabasic substrates. Plants collected from Salajar Island were shown to contain anomalously high concentrations of copper possibly due to anomalous copper concentrations in the soil.
Studies on plants that hyperaccumulate copper, cobalt and nickel : their potential for use in phytomining and phytoremediation : a thesis presented in partial fulfillment of the requirements for the degree of Masterate of Science in Soil Science at Massey University
(Massey University, 1998) Bennett, Frances Anneli
This thesis reviews three lines of research on hyperaccumulators to examine their potential for phytoremediation and phytomining. The first line of research was to test the affect of nutrient addition on biomass and nickel uptake by two nickel hyperaccumulators, Alyssum bertotonii and Streptanthus polygaloides. Addition of fertiliser increased the biomass although the maximum amount added was found to be suboptimal. Nutrient addition did not affect the rate of nickel uptake. Larger plants contained a more dilute nickel content but still had an overall larger amount than smaller plants. The second line of research was to test the affect of chelates on metal uptake by copper and cobalt flora of the Democratic Republic of Congo (formally Zaïre) and a copper tolerant plant from Spain, Erica andevalensis. EDTA and Citric Acid increased uptake of copper in these plants but had no effect on the uptake of cobalt and nickel. EDTA increased the uptake of lead by Alyssum bertotonii but did not affect the uptake of zinc and cadmium. The third line of research was to examine the reality of hyperaccumulators of copper and cobalt. Copper and cobalt hyperaccumulation does in fact exist but not to the extent reported previously. There is a good possibility that the previously reported values for copper and cobalt hyperaccumulation are in some cases erroneous due to high iron levels indicating contamination of plant samples by soil.
Environmental implications of phytoextraction for mercury and gold : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Earth Science
(Massey University, 2000) Msuya, Fletcher Abduel Msami
The overall objective of this study was to investigate how plants could be used to harvest gold (phytomining) and at the same time remove mercury (phytoremediation) from auriferous mercury-contaminated soils. This study was undertaken to find appropriate plants that could be used to harvest gold, residual in mine tailings or in uneconomic low-grade ore, and at the same time remove residual mercury, commonly used to extract the gold in artisanal mining areas. Different procedures involving analytical methodology, leaching of acid mine tailings and the growing of plants in both gold and mercury-bearing substrates were undertaken. The analytical methods involved in the analysis of gold in the laboratory using the modern instruments were Flame Atomic Absorption Spectrometry (FAAS) and Graphite Furnace Atomic Absorption Spectrometry (GFAAS). The determination of mercury involved using Flameless Atomic Absorption Spectrometry. To understand the induced solubility of metals in phytoextraction, Tui mine tailings were leached with several chemicals known to solubilise gold: ammonium thiocyanate, ammonium thiosulphate and urea. The pH of the tailings material was varied through amendment with lime to examine the effect of this geochemical parameter on metal solubility and thus the potential for both plant uptake and leaching. The Tui mine tailings were chosen because of their geochemistry; these are highly weathered sulphide-ore tailings that leach heavy metals into adjacent water systems. The induced-phytoextraction potential of root crops was also examined in this thesis. Five root crops were grown in an artificial substrate consisting of 3.8 mg/kg (ppm) of elemental gold dispersed in sand. The possibility of using these root crops for phytomining was determined by separately adding chelating agents ammonium thiocyanate and ammonium thiosulphate to the substrate. In most cases there was a higher gold concentration in the roots than in the shoots. The highest mean gold concentrations were found in carrot roots and in roots of two radish cultivars. It was concluded that there was some potential for the use of carrot to grow an economic crop of gold from mine tailings. Results obtained from experiments where plants were grown in Tui tailings indicated that both chicory and Brassica juncea could be used for the phytoextraction of gold and mercury in the same crop. Under acidic conditions thiocyanate induced the uptake of gold by Brassica juncea and the uptake of mercury by chicory; and thiosulphate induced the uptake of mercury by chicory, but it did not induce the uptake of gold by the same plant. Under alkaline conditions, treatment with ammonium thiosulphate induced the uptake of gold and mercury by Brassica juncea; and treatment with thiosulphate induced the uptake of mercury by chicory but it did not induce the uptake of gold. It was therefore concluded that, Brassica juncea could be used for phytoextraction of gold and mercury when ammonium thiosulphate is applied to the substrate. Results from the root-crop experiment indicate that, carrots could supersede most of the plants used due to the greater apparent metal-uptake potential. Finally, a model is proposed for field trials to examine the potential of phytoextraction for gold and mercury in Tanzania. The aim of this model is to examine how the positive results obtained from research conducted in the laboratory and greenhouse can be put into practice. The use of similar plants as well as traditional tropical species (e.g. wild cassava - a known accumulator of cyanide) is suggested along with suitable chemical amendments.
Phytoextraction of palladium and gold from Broken Hill gossan : a thesis presented in partial fulfilment of the requirements for the degree of Master of Environmental Management at Massey University, Manawatū, New Zealand
(Massey University, 2015) Aquan, Hendra Michael
The research in this thesis was conducted as part of the Phytocat Project; a collaborative effort between University of York (UK), Yale University (USA), University of British Columbia (Canada) and Massey. The aim of the Phytocat project was to yield a target concentration of 1,000 μg g-1 palladium in plants, so that the plants could be used as catalysts in chemical reactions. This thesis focussed on the phytoextraction of palladium from Broken Hill gossan, a platinum group element-rich rock collected from Australia. The gossan and surrounding soil has an elevated concentration of iron, copper, nickel and precious metals. Samples of species native to the Broken Hill gossan and the associated rhizosphere soil were collected from the field and analysed to screen natural levels of metal accumulation in plants of the area. Five native plant species were identified: Solanum centrale (bush tomato), Brassica sp, Ptilotus obovatus (silver tail), Sclerolaena lanicuspis (copper burr) and Tetragonia moorei (annual spinach). The copper concentration in all plant tissues had a strong relationship with copper in soil. An individual Solanum centrale plant recorded a copper concentration of 277 μg g-1 from soil with concentration of 796 μg g-1 suggesting that this species is a copper tolerant plant from Broken Hill. No anomalous levels of nickel were recorded in plant tissues. The average palladium concentration measured in the rhizosphere soil was 28.8 ng g-1. However, the five native plant species could not concentrate palladium in their biomass. Solubility of palladium was suggested to be poor in natural environment. To study the potential of induced hyperaccumulation to increase the palladium uptake in plants, 60 kg of gossan from the field was collected, crushed and used as a plant growth medium for controlled plant trials at Massey University. Two types of gossan rock were collected, classified by the dominant form of iron oxide mineral in the rock structure: goethite dominated (soil A) and hematite dominated (soil B). The goethite material (A) has a higher total and soluble metals concentration than the hematite mateiral. Initial trials focused on Brassica juncea. However, despite germinating, this plant grew poorly on both types of gossan. Insifficient biomass was available to induce uptake of metals, and therefore only the natural levels of metal uptake in the poorly developed plants was quantified. Total harvested aerial biomass was 5.1 g from 39 pots each containing 800 g of gossan. The mean metal concentrations in plants grown in the two soils was not significantly different (p< 0.05). The concentration of palladium in the plant biomass ranged from 2,130 to 2,909 ng g-1. This study proposed that 1,000 ng palladium g-1 is a suitable hyperaccumulation threshold level and therefore B. juncea on the gossan was able to hyperaccumulate palladium. The average copper concentration in the biomass was 759 μg g-1 and it is likely that high copper solubility in the growth substrate affected plant growth performance. A second trial used Cannabis sativa (Hemp) due to recorded metal tolerance of this species. Pots were re-seeded with C. sativa. Hemp germinated and grew well relative to B. juncea. Potassium cyanide solution (50 mL of 8 g L-1) was applied to each pot at the point of maximum biomass to induce the solubility of precious metals and therefore to induce hyperaccumulation. Significant metal concentration values after KCN treatment were as follows: Copper (6,726 μg g-1) > nickel (184 μg g-1) > palladium (62 μg g-1) > gold (9 μg g-1). Following established criteria values, copper, palladium, and gold hyperaccumulation was observed. The mean metal concentrations of copper, nickel, and palladium from Hemp grown in soil B were greater compared to Hemp grown in soil A and control plants (p < 0.05). However, gold concentration between Hemp A and Hemp B was not different significantly (p > 0.05). These results were anomalous compared to the recorded total and soluble metal concentration of the two rocks. This study concluded that total metal in soil is not an indication for metal concentration in plant tissues. Accumulated metal in plants is a function of the concentration of soluble metal in soil that can be readily absorbed by plants. Different characteristics of the substrate (in this case iron oxide) may influence metal uptake in plants. Iron oxide minerals were identified as plant competitors for soluble metals in soil solution. In this case, goethite adsorbs more soluble metal ions than hematite and therefore plants grown on the goethite substrate accumulated less metal relative to the hematite soil despite the goethite rocks having a greater total and soluble metal concentration. Metal tolerance was also highlighted as an important factor in the induced accumulation of palladium. Palladium is often associated with copper in soils and tolerance to copper is a key factor. In this work, Brassica juncea was proven less tolerant to copper than C. sativa. The target of 1000 μg g-1 palladium in plants has not yet been reached but the Broken Hill gossan is highlighted as a useful substrate for ongoing work. There is good potential to test the native copper tolerant species Solanum centrale, for induced metal uptake in the future.
Aspects of the accumulation of cobalt, copper and nickel by plants : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry, Massey University
(Massey University, 1980) Morrison, Richard Stephen
Hyperaccumulation of heavy metals was studied with the intention of elucidating the mechanisms of tolerance of hyperaccumulator plant species. Two main areas are covered; cobalt and copper accumulation by plants from Shaba Province, Zaïre, and nickel accumulation by species of the genus Alyssum. In surveys of vegetation of metalliferous soils of Shaba, nine or ten new hyperaccumulators of cobalt were discovered along with eight or nine very strong accumulators. For copper, seven hyperaccumulators and five or six very strong accumulators were discovered. Some families contained a higher frequency of hyperaccumulators than others. There is also a difference in superorder classification of cobalt and copper hyperaccumulators on one hand and nickel hyperaccumulators on the other. Surveys of the genera Aeolanthus, Ipomoea and Pandiaka were made but only one new copper hyperaccumulator was found: no new cobalt hyperaccumulators were found. Several species had their abilities to accumulate confirmed. Pot trials on three hyperaccumulators Aeolanthus biformifolius, Haumaniastrum katangense and H. robertii, showed accumulation of cobalt but not the expected accumulation of copper. The uptake curve was of the exclusion-breakdown form. The limit of breakdown, for each metal, was similar from species to species. Cobalt was less readily excluded than copper. The tolerance tests showed that some species have individuals with greatly enhanced abilities to survive higher metal concentrationsthan is normal for that species, while other species have more uniform tolerances. There appears to be no requirement for large metal concentrations at germination and seeds germinate more readily in the absence rather than the presence of the metals. The distribution of cobalt and copper within leaf tissues, of five species, appears to be parallel within each species. For each metal, the distribution is parallel between different species with the exception of Buchnera metallorum. More detailed studies on cobalt in H. robertii showed the distribution to be even over the leaf area but with small anomalous regions of high concentration. The possibility that some of the cobalt was precipitated as oxalate crystals is considered. The water-soluble cobalt fraction ligand could not be identified but was not proteinaceous. It has a mass of 5,200 g per mole of cobalt. A survey of the genus Alyssum revealed thirty-four taxa as hyperaccumulators to add to the fourteen previously known. All the taxa are from section Odontarrhena. The geographical distribution of the hyperaccumulators is discussed as is the possible evolution of hyperaccumulators in subsections Compressa and Samarifera from non-accumulators within them. Studies of nickel accumulation by eleven Alyssum species and the closely related Bornmuellera tymphaea showed similar characteristics for all hyperaccumulators but two non-accumulators differed. A rise-to-saturation uptake form was noted. In the absence of nickel, cobalt could be accumulated with a similar uptake form. Cobalt accumulation in the presence of nickel is unknown. The rate of uptake is relatively rapid. The tolerance of hyperaccumulators to high nickel concentrations was confirmed in two types of tolerance tests; a substrate medium test and a solution test. The results from the two tests are compared. The distribution of nickel between the plant organs is discussed. The analysis of mineral elements in leaf material showed interesting differences between hyperaccumulators and non-accumulators for calcium, magnesium and manganese content but these could not be related to differing nickel concentrations. A similar find was made for glucosinolates. An organic acid survey was restricted by the non-identification of many acids. Separation of the nickel complexes was made. Identification of ligands involved in nickel complexatian was attempted but few positive results were found. Two ligands were common in significant quantities for all species studied. The results of these experiments were used to discuss possible evolution of hyperaccumulator species both in terms of their superorder distribution and their method of metal ion uptake. An equilibrium mechanism of uptake is proposed which involves a multiplicity of complexes for the ion absorbed. The mechanism differs from that which is commonly proposed for micronutrient elemental uptake.
The phytoextraction of heavy metals from metalliferous soils : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University
(Massey University, 1997) Robinson, Brett Harvey; Robinson, Brett Harvey
This study concerns the investigation of the potential use of plants to remove heavy metals, in particular nickel, zinc and cadmium, from soils. The study is divided into three sections, bioavailability, phytomining, and phytoremediation. The effect of various extractants on the solubility of heavy metals in some soils was tested. It was found that the solubility of the metal invariably increased as the pH of the extractant decreased, and as the concentration of the extractant increased. These relationships could be predicted mathematically. It concluded that a more concentrated, neutral, non-chelating extractant such as 1M ammonium acetate, is the most suitable for estimating bioavailability. An investigation into the addition of some compounds to soils to increase metal solubility showed that EDTA and citric acid should maximise solubility while keeping soil parameters (pH, osmotic potential, nutrient availability) within the growth range of the plant. These compounds are also relatively inexpensive. The effect of bioavailable elements on a New Zealand serpentine flora was investigated with regard to the soil's potential for phytoextraction. It was found that nickel was the only element that would be suitable for phytoextraction from these soils. The relative infertility of the serpentines was attributed primarily to the toxic effects of magnesium and/or nickel. Removing nickel from the soil by phytoextraction may enable the soil to be used as a magnesium-rich fertiliser. The potential of the hyperaccumulator plants Alyssum bertolonii and Berkheya coddii for nickel phytoextraction was studied. With the addition of fertilisers, the plants could remove respectively in excess of 72 kg and 100 kg of nickel per hectare per annum. Were the metal to be sold, and energy from the plant's incineration utilised, the net profit per hectare would be greater than that of a crop of wheat. Both of these plants re-grew after harvesting without the need to re-sow. In the case of B. coddii, the nickel concentration in the regrowth was more than twice that of the original crop. Phytomining for nickel is a viable proposition provided the operation is carried out over a large area. The nickel concentration in the plants was logarithmically related to the nickel extracted by a 1M ammonium acetate extract. Theoretical nickel yields from various soils could be predicted by performing a 1M ammonium acetate extraction on the soils. About half of the soils tested from various locations around the world contained enough soluble nickel to be economically phytomined. Alyssum bertolonii and B. coddii also have the potential to remove nickel from polluted soils. The addition of EDTA and citric acid to the soil in which the plants grew actually decreased the nickel concentration in the plants despite increasing the nickel solubility in the soil. The economics of phytomining are closely linked to the value of the metal. Cobalt and possibly even the noble metals could be economically phytomined at low concentrations in plants: a fertile area for future research. Sequential extractions were used to model the effect of successive hyperaccumulator crops on the bioavailability of nickel in ultramafic soils from around the world. The nickel concentration in all of the soils tested, decreased in a regular manner and could be predicted mathematically. Assuming an initial nickel crop of 100 kg/ha, the number of nickel crops above 70 kg/ha that could be obtained was calculated for each soil. The number of economic nickel crops varied between 3 and 18 before the soil would have to have been modified to increase nickel bioavailability. The possibility of removing zinc and cadmium using Thlaspi caerulescens showed that the plant has a potential use for removing cadmium from weakly polluted soils. The low bioaccumulation factor for zinc accumulation means that this element will never be removed in a reasonable time span. The concentration of both zinc and cadmium in the plant could be predicted by the extractable fraction in the soil as estimated by using 1M ammonium acetate as extractant. It was concluded that phytomining and phytoremediation are feasible possibilities under certain conditions. (1) Metals necessarily have to be slightly soluble in the soil before they can be phytoextractcd. Metal solubility may be improved by the addition of chemicals such as chelating agents. (2) Due to relatively low yields, phytomining will only be viable for more valuable elements where the concentrations in soils are too low for conventional mining. (3) Phytoremediation will be most effective on weakly polluted soils. (4) The economics of phytoextraction favour its use over large areas. The amount of metal able to be extracted from an area can be predicted by performing an extraction with 1M ammonium acetate.

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