WO2003045594A1 - Medium and method for treating tailings of mining activities - Google Patents

Abstract

This invention provides a medium and method for treating tailing bodies of mining activities including the steps of vermicomposting a mixture of wood particles and sewage; applying the mixture to the tailing bodies; and planting vegetation on the tailing bodies.

Description

MEDIUM AND METHOD FOR TREATING TAILINGS OF MINING ACTIVITIES

INTRODUCTION AND BACKGROUND This invention relates to a medium and method for treating tailings of mining activities.

Anthropogenic activities, such as mining, produce large amounts of wastes that create economical and environmental problems. This is owing to large areas of land needed to dispose of the wastes, which are not only expensive, but the wastes also contaminate soil, groundwater and air. In particular, the mining of platinum, gold and other minerals has a considerable environmental impact owing to the development of large tailing dams. The tailings are generated as a slime waste stream during mineral processing and are essentially a biologically sterile medium with limited water holding capacity and a high base saturation percentage. The tailings also contain, amongst others, high concentrations of potentially environmentally toxic heavy metals that can leach to the groundwater.

Investigations by Walmsley (1987) showed that although the tailings are not saline, they contain high concentrations of manganese, iron, and sulphur, which may be phytotoxic in high concentrations. Platinum tailings, for example, consist mainly of sand (75%) and silt (20%) with the remaining 5% of the particles being a clay and negligible organic fraction. The above factors therefore complicate the proper revegetation of the tailings to the pre- mining land use potential and lead to environmental degradation of the region. In addition to inorganic tailings, platinum mines further produce large amounts of organic wastes viz. Saligna eucalyptus wood chips and sewage sludge. Tailing dams pose a range of environmental dangers including air, dust and groundwater pollution, due to its physical and chemical properties, whereas dumped wood chips pose a fire hazard during the hot and dry summer months.

The wood chips that are created during extraction of platinum originate from underground blasting with wood buttresses intact. The result is that wood chips and ore are processed together during the initial milling and extraction phases of the mineral processing. The wood chip fraction is separated as a by-product, through screening, prior to platinum extraction. Owing to blasting, the wood chips contain a high concentration of nitrate to an extent that the nitrate concentration is high enough to cause health problems, such as methaemoglobinaemia if leached into the groundwater (DWAF 1996). At present, wood chips are incinerated at high cost.

The slimes, wood chips and sewage therefore present an ecological and environmental liability to mines. -51/27

A main goal in tailings remediation projects is to return the site to its precontamination condition, which often includes revegetation to stabilise the treated soil. This is both difficult and expensive because of the unavailability of potential topsoil as well as deficiency in organic matter, elemental imbalances, and absence of essential nutrients in tailing dams. In an attempt to address these problems, topsoil is imported from other areas (that then requires rehabilitation) or periodical treatment with inorganic fertilisers, which are both expensive and not ecologically sustainable. Most tailing dumps are currently rehabilitated by vegetating the dumps with grass. The promotion of a viable and sustainable vegetation cover is, however, a problem owing to infertility and phytotoxicity of the growth medium.

USA patent number 6,004,069 discloses a method for providing a subaerial inorganic composite capping cover over sulphide containing tailings and sulphide bearing mine waste materials, comprising the steps of:

i) providing a deposit of sulphidic particulate material comprising at least one of the group consisting of sulphide mineral containing tailings, sulphide bearing waste rock and sulphide bearing mine waste material, said sulphidic particulate material having low hydraulic conductivity, said deposit having a peak and a slope enclosing an angle greater than 0.5 degree with the horizontal; -50/27

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ii) depositing a first particulate layer over said deposit of sulphidic particulate material, said first particulate layer comprising an inert, fine substance having average particle size between 10 Em and 200 .mu.m and hydraulic conductivity higher than 10.sup.-7 cm/sec, matric suction value greater than 4 cm of water, said first particulate layer being deposited to yield said first particulate layer extending over said deposit of sulphidic material in depths in excess of 4 cm;

iii) depositing a second particulate layer over said deposit of sulphidic particulate material, said second particulate layer comprising an inert, fine-granular substance, having average particle size between 200

.mu.m and 5000 .mu.m, hydraulic conductivity between 10.sup.-3 and

1 cm/sec, the hydraulic conductivity of said second particulate layer being at least one order of magnitude higher than the hydraulic conductivity of said first particulate layer, and a matric suction value, the ratio of the matric suction value of said second particulate layer to the matric suction value of said first particulate layer being less than

1 :2, said second particulate layer being deposited to provide said second particulate layer extending over said first particulate layer to a depth which is at least 1.5 times the matric suction value measured in cm of water, of said second particulate layer; and, -49/27

iv) depositing a third particulate layer over said deposit of sulphidic particulate material, said third particulate layer comprising an inert, coarse-granular substance, having average particle size greater than 3 mm and hydraulic conductivity higher than 1 cm/sec, said third particulate layer being deposited to provide said third particulate layer extending over said second particulate layer in depths in excess of 6 cm.

The inert, fine substance comprised in said first particulate layer is selected from the group consisting of oxidic mill tailings, low-sulphide containing mill tailings, desulphurised mill tailings, neutralised mill tailings, loess, fine sand, sandy clay, sandy loam, fly ash, silt, glacial till, fine materials of alluvial origin and mixtures of these.

The inert, fine-granular substance comprised in said second particulate layer is selected from the group consisting of granulated slag, granulated desulphurised slag, desulphurised rock, fine gravel, finely crushed rock, winter sand and mixtures of these.

The inert, coarse-granular substance comprised in said third particulate layer is selected from the group consisting of crushed rock, crushed stone, crushed limestone, pebbles and naturally occurring coarse materials, crushed demolition material and mixtures thereof. -48/27

Some of the disadvantages of the above method are that no organic matter is added to the top layers and that it is a relatively complex and expensive process involving numerous different substances and steps. It is therefore not commercially viable.

OBJECT OF THE INVENTION

It is accordingly an object of the present invention to provide a medium and method for treating tailings with which the aforementioned problems and disadvantages may be overcome or at least be alleviated.

SUMMARY OF THE INVENTION

According to a first aspect of the invention a method is provided of treating a tailing body of mining activities including the step of applying wood particles to the tailing body.

The wood particles may be wood chips recovered from waste timber and which may be a by-product of mining activities, more particularly in the form of timber mine props disintegrated in blasting operations.

The wood chips may be pre-treated with an acid.

The acid may, for example be nitric acid (HNO₃). the chips may be applied to a top surface of the tailing body, for example in the form of a coating.

In one preferred form of the method, the chips are worked into the tailing body, for example by digging the chips mechanically and/or manually into the body.

The chips are preferably worked into the body to a level of about 30cm below an outer surface of the body.

The chips may be applied to an existing tailing body in the form of a dam to rehabilitate the dam.

However, in one preferred form of the method, the chips are intermittently applied to a tailing dam during the development thereof.

The wood chips are preferably applied at a rate of between 60 to 90 tons per hectare of tailing dam surface.

Further according to the invention the method includes the further step of composting the wood chips prior to the step of applying the wood chips to the body. -46/27

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Yet further according to the invention the step of composting the wood chips includes the step of vermicomposting the wood chips.

The step of composting the wood chips may include the further step of mixing the wood chips with another source of organic material.

The other source of organic material may comprise sewage.

The wood chips and sewage may be mixed and allowed to form compost, after which the compost may be inoculated with worms and allowed to form a vermicomposted medium.

The worms may be from the species Eisenia fetida.

The wood chips and the sewage may be mixed in a ratio of 3:1 or 3:2 if the availability of the latter is not a limiting factor.

According to another aspect of the invention there is provided a tailings dam treated according to the above method of the invention.

According to yet another aspect of the invention there is provided a medium for the treatment of tailing bodies of mining activities comprising a mixture of -45/27

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wood particles and another source of organic material, which has been composted.

The wood particles may be wood chips recovered from waste timber, which is a by-product of mining activities.

The wood chips may be in the form of timber mine props disintegrated in blasting operations.

The other source of organic material may be in the form of sewage.

The mixture may further be vermicomposted.

The medium may further include a selection of micro-organisms.

The invention will now be described further, by way of a plurality of examples, with reference to the accompanying figures and tables. For the sake of clarity, the descriptions of the sets of figures are each time set out at the associated example. -44/27

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EXAMPLE 1

This example makes reference to the following enclosed drawings wherein :

Figure 1.1 is a flow diagram of the method according to the invention; and

Figure 1.2 is an end view of a tailings dam showing grass growing on sides thereof to rehabilitate the dam.

A mining method including the method according to the invention of treating or rehabilitating a tailing dam of the mine is generally illustrated by the block and flow diagram in Figure 1.1.

The mine may, for example, be a platinum (Pt) mine 10. The product mined and waste, including wood particles in the form of wood chips or pieces of timber, are shown at 12. The pieces of timber originate from well-known timber mine props that are disintegrated during blasting operations in the mine. This mixture is fed to a floatation stage 14 where the lesser dense waste timber is separated in known manner from the more dense platinum and slurry.

The platinum and slurry mixture at output 16 are separated at 20 also in well- known manner. The platinum is recovered at 22 and the remaining slurry is -43/27

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pumped at 24 to a remote location to develop into a tailing dam 26, also in known manner.

The waste timber at output 18 of the floatation stage 14 is crushed and rolled at 28 into resulting timber chips 30.

It has been determined that the known tailing dams comprise unacceptably high concentrations of water intractable elements, which are leached out by rainwater and carried into underground water resources, thereby polluting those water resources. In table 1.1 there are shown elemental fractions in a sample of the timber chips and a sample of the tailing dam respectively that are water-soluble and that may be moved as hereinbefore described and which were determined by a known extraction procedure.

In table 1.2 there are shown elemental fractions corresponding to that in table

1.1 for a mixture wherein the timber chips 30 are applied to the tailing dams 26 as shown at step 32 in figure 1.1.

From the results of the analysis conducted on the wood chips and tailings separately, it is clear that the macro-elemental concentrations of the tailings contain high calcium (Ca), magnesium (Mg), sodium (Na), sulfate (SO₄) and chlorine (CI) concentrations. The high SO₄ content in the tailings is indicative of a definite acid generating capability over time. This is corroborated by the -42/27

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low bicarbonate (HCO₃) concentrations left in the sample, indicating that the buffer capacity within the tailing has almost been depleted. The need for an increased adsorption capacity is also revealed both by the high base saturations of 21.48% and high electrical conductivity (EC) of 2.09 mS cm^"1, implying that those elements not currently bound would be carried by any rainfall through the dam into the groundwater. Of the micro-elements both the zinc (Zn) and manganese (Mn) concentrations exceed the recommended norm values as well as the potentially toxic heavy metals aluminium (Al), nickel (Ni), cobalt (Co) and arsenic (As) all of which are typified by high concentrations in the tailings. In contrast, the timber chips, although containing high Al concentrations, offer a means of adsorbing some of the excessive elemental concentrations.

It is known that negative surface charges on the timber chips attract and bind certain elements and the results in table 1.2 clearly indicate a trend of decreasing Ca, Mg, K, Na, SO₄, CI, Mn, Cu, Zn, Ni and Co concentrations with increasing timber chip application rates. The lowering of the aforementioned elemental concentrations in the extractable water fractions is also clearly reflected by the lower electrical conductivity (EC) with the application of increasing volumes of timber chips. Consequently, the concentrations of elements potentially available to leach down into the groundwater become progressively less as the timber chip application rates are increased. -41/27

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It has been found that pre-treating the timber chips with a 0.01% nitric acid (HN0₃) solution could result in lower application rates of timber chips with the same efficiently in lowering potentially toxic elemental concentrations.

Also, as described in more detail in Example 5 below, the prior vermicomposting of the wood chips (with or without the inclusion of sewage sludge) increases the bulk density of the material that has to be applied to the tailings and reduces the composting time period.

It has further been found that an application rate of between 60 ton to 90 ton wood chips per hectare of tailing dam surface produce good results.

Referring to Figure 1.2 where a tailings dam 26 is shown, the acid pre-treated timber chips should be worked into the tailing dam 26 to a level 34 of about

30 cm below an outer surface 36 thereof. The wood chips are preferably intermittently worked into the settled sides of the dam as the dam develops over a period of time.

It is believed that negative surface charges on the timber chips significantly increase the cation exchange capacity (CEC), thereby reducing the movement of potentially toxic elements into the groundwater. -40/27

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The tailings may further be rehabilitated by sowing grass seeds on the aforementioned sides. It is foreseen that with the level of nitrates present in the dam sides 38 including the timber chips, less or no inorganic fertilizer would be required to promote the growth of the grass 40.

EXAMPLE 2

This example makes reference to the following enclosed drawings wherein:

Figure 2.1 is a schematic layout of treatments and replications in

the method in accordance with the present invention,

on platinum slimes; and

Figure 2.2 depicts a RDA biplot indicating the relationship between wood chip applications (0, 5, 15 and 30 ton ha^"1) on the nutrient availability of the growth medium. The species environmental correlation for the first axis was 0.749.

Experimental design

An experimental site was constructed at a platinum tailings dam and consisted of 24 x 4 m², plots that were monitored for one and a half years. -39/27

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The respective layouts of the different treatment groups are summarised in Figure 2.1. The experiment consisted of six treatments with three replicated plots and four control plots.

Treatments 1 -3

The first three treatments used a combination of the present revegetation practices at the mine and fertilizer application according to standard practice, but with increasing wood chip application (Treatment 1 : 5 ton ha^"1; Treatment 2: 15 ton ha^"1; Treatment 3: 30 ton ha^"1). A mixture of wood chips treated with Zantate and untreated wood chips were used at a ratio of 1:1. The following fertilizers were applied to the first three treatments: a) Super Phosphate 1200 kg ha^"1 b) NH₄SO₄ 350 kg ha^"1 c) KCI 400 kg ha^"1

The first three treatments were revegetated with a mixture of Cynodon dactylon and Cynodon nlemfuensis stolons and rhizomes collected in the vicinity of the tailings dam. The Cynodon dactylon and Cynodon nlemfuensis were planted in equal proportions in six rows per plot.

Treatment 4

The fourth treatment was ameliorated with 30 ton ha^"1 wood chips and the fertilizer application as used in the first three treatments. Plots were -38/27

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revegetated with the seed mixture consisting of Cenchrus ciliaris (Molopo) at 10 kg ha^"1, Chloris gayana at 10 kg ha^"1, Eragrostis curvula (PUK E436) at 5 kg ha^"1 and Eragrostis lehmanniana at 5 kg ha^"1.

Treatment 5

Treatment 5 was ameliorated with 30 ton ha^"1 wood chips and the fertilizer application as used in the previous treatments. The seed mixture consisted of a mixture of 5 pioneer grass species, 5 perennial grass species and 3 potential creeping grass species (Table 2.1).

Treatment 6

Treatment 6 was ameliorated with 30 ton ha^"1 wood chips. Chemical analyses of the tailings (Table 2.5) were used to determine the fertilization rate for optimum growth conditions. A fertiliser application of 800 kg ha^"1 Mono Ammonium Phosphate (MAP) was applied to improve the nutritional status of the growth medium. The plots were revegetated with a similar grass seed mixture used in Treatment 5 (Table 2.1 ).

Materials and methods

Botanical surveys

The vegetation on the site was monitored frequently using a bridge point apparatus mounted on a 1 m² frame. Species frequency and basal cover of -37/27

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the species were therefore determined using 125 points m^"2. The standing grass biomass was subsequently determined. The standing biomass rooted in 1 m² quadrant was clipped using sheep shears and sorted according to species. The biomass was dried at 60°C for 48 h and weighed.

Soil sampling and analysis

Soil samples (approximately 500 g) were collected using a soil auger. A fifty- gram sub sample was used for quantifying the particle size distribution according to the procedures advocated by the American Society for Testing and Materials (1961 ). The soil samples were chemically analysed by means of a 1 :2 (v/v) extraction procedure as described by Black (1965) for the determination of the water-soluble basic cation fraction, (Ca, Mg, K and Na) and trace elements (Fe, Mn, Cu and Zn) as well as heavy metals (As, Se, Al, Cr, Co, Ni, Pb and Cd).

The water soluble basic cations (Ca, Mg, K and Na), trace elements (Fe, Mn, Cu, Zn) and heavy metal (As, Se, Al, Cr, Co, Ni, Pb and Cd) were quantified by means of atomic absorption spectrometry with a Spectr. AA - 250 (Varian, Australia). The anions (F, CI, NO₃, PO₄ and SO₄) was quantified with an Ion Chromatograph (Metrohm 761 , Switzerland). A 75 ml of soil was used for the

1 :2 extraction analysis. Ammonia (NH₄) concentrations were quantified by means of the ammonia-selective electrode method as described by Banwart et al., (1972). The bicarbonate (HCO₃) content in the soil was determined by -36/27

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means of the potentiometric titration method with an end-point of pH of 4.5 with a standard 0.005M HCI solution (Skougstd et al., 1979). Boron (B) concentration was colorometrically determined by means of the azomethine- H-method described by Barrett (1978) using a VEGA 400 spectroquant at an absorbancy of 420nm.

The pH value and electrical conductivity (EC) of the soil was determined in the 1 :2 extract with a WTW LF92 conductivity meter at 25°C.

Vegetation, soil and water chemical data were analysed using STATISTICA ver. 6 (StatSoft, Inc. 2001 ). The influence of the treatments and wood chips concentrations were investigated with ReDundancy Analysis (RDA) (Ter Braak and Smilauer, 1997). RDA is a constrained linear ordination method and therefore also a direct gradient analysis technique which integrates ordination with regression (Ter Braak, 1994). The advantage of using ordination and direct gradient analysis as analysis tool is it provides a graphic result of the relationship between variables and relevant environmental factors. The screening benchmarks set by the USA Department of Energy (Efroymson et al 1997) was used as toxicological guideline. -35/27

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Results

Plant composition Table 2.2, 2.3 and 2.4 summarise the species frequencies, basal cover and biomass measured at the six treatments and the control plots. Fourteen grass species were encountered during the survey period. The treatments with the highest species richness were Treatments 5 and 6, which were seeded with a species mixture indicated in Table 2.2. The seed mixture used in Treatment 4 produced the highest total basal cover (5.2%) All other treatments, including the control, had a very similar basal cover ( ± 3%). The total biomass between plots were not significantly different due to the high variance in standing biomass. The total biomass was the greatest in plots treated with Treatment 6. This was largely due to the vigour of Cenchrus ciliaris.

According to frequency, basal cover and biomass results, Cenchrus ciliaris variety Molopo was the most successful species to establish from seed. Other species that also performed satisfactory were Cenchrus ciliaris variety Gayndah (Treatment 6), Eragrostis lehmanniana (Lehmann's Love Grass)

(Treatments 4-5J and Eragrostis curvula (Treatments 4). It is surprising that Digitaria eriantha (Smuts Finger Grass), which generally does very well on rehabilitated areas (Mentis 2000) did not establish in the experimental plots. -34/27

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A probable reason for the unsuccessful establishment of Digitaria eriantha is the drought conditions during the beginning of the experiment.

Soil chemical properties

Three samples were taken from the tailings to quantify the chemistry and to determine the fertiliser application for Treatment 6 (Table 2.5). Samples two and three were very similar in chemistry but the nutrient concentrations in sample one were considerably greater than the first two samples. This indicates the high variability in chemical composition of the samples. The 1 :2 water extraction (Table 2.5) further indicated that heavy metal phytotoxicity may be a serious problem in unamended tailings. Plant growth may be affected as a result of elevated soil solution concentrations of Pb, Cr, Co, Se and especially As (Efroymson 1997).

Results from the 1 :2 water extraction procedures presented in Table 2.6 gives an indication of the element concentrations in the soil solution that were available for adsorption by plants during February 2002. In general the macro element concentrations (Ca, Mg and K) were slightly lower than is preferred for efficient growth. The available phosphate and nitrate in the soil solution have also been depleted due to assimilation by plants. Concentration of NO3 and PO₄ will be a limiting factor for plant growth. -33/27

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Except for Cu, no potential micro nutrient toxicity may occur at the present pH level. Cu occurred in elevated concentrations as high as 0.827 μmol/dm³

(the potential level for phyto toxicity is according to Efroymson (1997) 0.94 μmol/dm³).

The pH of the growth medium remained alkaline (average pH for all treatments: 7.8 + 0.025). The low EC also confirms the low nutrient status of

the growth medium and further indicates that salinity is not a concern. The sodium adsorption ratio SAR was also lower than the recommended value of 1 indicating that no potential soil sodicity exist.

By comparing Table 2.5 with Table 2.6 it is possible to determine changes in the chemical properties of tailings due to time, vegetation growth and application of wood chips. All macro element concentrations in the tailings decreased considerably. The sulphate concentrations remained relatively the same or decreased slightly in the control plots and plots treated with lower concentrations of wood chips. The sulphate concentrations in the growth medium solution also decreased considerably in Treatment 6, which were atypical in comparison to the other treatments also treated with 30 ton ha^"1 wood chips. The concentration of the microelements Fe, Mn and Cu increased indicating an increase in the solubility of these elements. Zinc and boron, however, decreased in concentration. The pH in the soil solution remained relatively the same in the region of 7.8. The electrical conductivity also decreased considerably from an average of 2.267 mS/cm (unamended tailings) to 0.296mS/cm at the end of the study period.

To elucidate the effect of increasing wood chip applications on the chemistry of the tailings, a RDA was performed and the results are graphically displayed in a RDA biplot of species (chemical variables) against wood chip applications as factor (Figure 2.2). Because only one variable is tested the canonical axis and the species ordination axis are presented on the first ordination axis. The chemical variables as species correlated 74.9% with the wood chip application as environmental factor. According to Figure 2.2, chemical variables best associated with the wood chip application gradient was B, P and Cu (positively correlated) and pH (negatively correlated). The pH of the medium will acidify with increase in wood chip application and the concentration of B and especially Cu will increase. Because macro nutrient concentrations (Ca, Mg, K, Na, SO₄) and electrical conductivity (EC) were weakly associated with the first ordination axis these variables were in lesser extent influence by increase application of wood chips.

Table 2.7 presents a correlation matrix between the soil chemical variables. Salinity in the growth medium can be attributed mostly to sulphates and especially calcium, potassium and magnesium sulphates. Calcium, magnesium and potassium were also highly correlated. Sodium was however better associated with chloride. Iron, manganese and copper were -31/27

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all correlated with each other. The only significantly negative correlation was between iron and ammonium.

Conclusion and recommendations According to the revegetation results a large number of species used especially in the high diversity mixture did not establish. The results indicated that a seed mixture of Cenchrus ciliaris, Eragrostis lehmanniana, Panicum maximum and Eragrostis curvula would suffice. Eleusine coracana was the most successful pioneer species. A possible explanation of the poor performance of the veld grass species is the low seeding rate of 1-2 kg/ha.

Seeds (of large seeded species) must be sown at a rate of not less than 5 kg/ha to ensure successful establishment. Tillers and runners of Cynodon dactylon and Cynodon nlemfuensis can also be planted at intervals for erosion control. The use of Cynodon dactylon instead of Cynodon nlemfuensis is preferred because it is indigenous to the area, more drought resistant and forms a more effective cover. Results also indicated that the seed mixture of Treatment 4 was more successful than the seed mixture of Treatment 5 and 6. In Treatment 4, less species were used, but it obtained the same results as the seed mixture used in Treatments 5 and 6. Both seed mixtures provided the same amount of cover and the basal cover of

Treatment 4 was higher than those of Treatments 5 and 6. The different seed mixture should also not influence the biomass production, according to results. The biomass was more influenced by the establishment of a -30/27

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particular species (in this case Cenchrus ciliaris) than by the total composition of the seed mixture.

The chemical growth conditions of the tailings improved considerably during the duration of the experiment. The biggest concerns regarding the soil nutrient status of the amended slime material are its low fertility and the possibility of micro element and heavy metal toxicity, especially copper, chromium, selenium and arsenic. Notwithstanding the possibility of phytotoxicity, the vigour and vitality of grasses seemed to be satisfactory. If the pre and post chemical composition of the tailings are compared, it appeared that the tailings are easily leached. This is probably an appreciable concern for groundwater pollution.

Because of the initial high concentration of nitrate in both the tailings and the wood chips, it was expected that the amended plots would have an elevated

NO₃ concentration, which was, however, not the case. A probable explanation for this is the high mobility of NO₃, which results in large amounts of NO₃ leaching out and the high rate of uptake by the vegetation, which explains the vigour in the vegetation (Mengel & Kirby, 1987). A further explanation is the immobilization of nitrogen owing to the high C/N ratio, causing some of the inorganic nitrogen to be fixed into organic nitrogen by soil micro-organisms (Tainton 2000). -29/27

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EXAMPLE 3

This example makes reference to the following enclosed drawings wherein:

Figure 3.1 depicts a graph of temperature (°C) profiles of composting and vermicomposting systems during the first 28 days. SS, sewage sludge; WC, woodchips; EM, micro-organism inoculate; e/w, earthworm;

Figure 3.2 depicts a graph of CO₂ (%) profiles of the composting and vermicomposting systems during the first 28 days. SS, sewage sludge; WC, woodchips; EM, micro-organism inoculate; e/w, earthworm; and

Figure 3.3: depicts a graph of O₂ (%) profiles of the composting and vermicomposting systems during the first 28 days. SS, sewage sludge; WC, woodchips; EM, micro-organism inoculate; e/w, earthworm.

Materials and Methods -28/27

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Organic wastes, earthworms and micro-organism inoculate

Air-dried samples of wood chips (WC) and sewage sludge (SS) were obtained from platinum mines. The earthworm (e/w) species used was Eisenia fetida ("tiger worm"), which is epigeic and is a potential waste composting worm (Edwards & Bohlen, 1996). The breeding stock of E. fetida used in this study was maintained on cattle manure at a temperature of ±25°C. Only mature clitellate worms were used for the purposes of this investigation. A commercial preparation of micro-organisms (EM^™) were

used in the inoculation experiments which consisted predominantly of Pseudomonas, Lactobacillus and Saccharomyces spp.

Composting and vermicomposting experiments

A mixture of WC and SS with a mixing ratio of 3:1 (dry weight kg^"1) was used. The dry ingredients were mixed and moistened with distilled water to a 70% (by weight) moisture content. Five treatment groups with three replicates each were investigated and consisted of WC+SS, WC+SS+EM, WC+SS+e/w, WC+SS+EM+e/w and WC mixtures. The substrate was put into plastic bins (60 x 40 x 30 cm), placed in an environmental chamber (25°C) and composted for a period of 28 days. In the treatments with earthworms, 100 mature worms were introduced after the 28-day composting period to avoid exposure of worms to the possible high temperatures during the initial thermophillic phase of composting. Physical and chemical parameters

From day 0 (refers to the time of initial mixing of the waste before decomposition) to 28 CO₂ and O₂ was measured with a portable CO₂ and O₂ analyser (Gas Data PCO₂), as well as the temperature. Whenever CO₂ increased or O₂ decreased beyond the levels of that in the air, aeration was manually increased to reverse this trend.

At the start and termination of the experiment total solids (TS), volatile solids (VS), ash contents, particle size distribution, NH₄ ⁺, NO₃ ^", NO₂ ^", pH, total and soil available P (P-Bray 1), total organic carbon (TOC), % lignin and

% cellulose were determined.

TS were determined as residue on drying at 80°C for 23 h and VS by ashing the dried samples at 550°C for 8.5 h (APHA et al., 1989). Particle size distribution was determined by sieving 100 g of material through a set of 4 sieves with screen-openings of 4.75, 4.00, 2.00 and 1.00 mm respectively. The particle sizes are reported in terms of geometric mean and geometric standard deviation as described in Ndegwa and Thompson (2001 ).

The anions NO3^", NO₂ ^" were determined by means of capillary electrophoresis (Waters Quanta 4000, Capillary Electrophoresis System, Waters, MA) as described by Heckenberg et al. (1989). NH₄ ⁺ concentrations were quantified by means of ammonia-selective electrode method as -26/27

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described by Banwart et al. (1972). The pH values of the substrates were determined in the 1 :2 extract with a calibrated pH meter (Radiometer PHM 80, Copenhagen) at 25°C after a 12-h equilibration period with intermittent stirring.

P_[totai] concentrations were determined colorimetrically using the vanadomolybdate method. This entailed pipetting 200 mL of digested sample solution into a 50-mL volumetric flask, adding 10 mL vanadomolybdate reagent into the flask and diluting it to volume with deionized water and mixing. After 10 min, the concentration was read on a colometric continuous flow analysis system (Continuous Flow Analysis System, Skalar, the Netherlands).

TOC was determined by an independent laboratory using the Walkley-Black method (Walkley and Black, 1934) and P-Bray 1 using Bray's extractant no. 1

(Bray and Kurtz, 1945).

% NDF, % lignin and % cellulose

The % NDF (neutral detergent fibre, i.e. the insoluble fraction of plant cells), % lignin and % cellulose were determined according to Rowland and Roberts

(1999). For the determination of NDF, samples were air-dried and ground

(<1 mm). The percentage dry material was determined by drying the air- -25/27

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dried samples for 3 h at 105°C and the dry weight correction factor

determined; i.e. ¹⁰%_/odry.

The reagent consisted of 18.61 g EDTA and 6.81 g Na₂B₄O₇ 0H₂O dissolved in 500 mL de-ionised water, whereafter 30 g sodium laurel sulphate

(SLS) and 10 mL 2-etoxyethanol were added. 4.56 g anhydrous Na₂HPO4 was separately dissolved in water, mixed with the other solution and finally diluted to 1000 mL.

0.5 g of the air dried material was placed into a 250-mL conical flask and 100 mL of the neutral detergent reagent was added. The solution was brought to the boil and simmered for 1 h. While still hot, the solution was filtered through a pre-weighed sinter (no. 2) whilst applying gentle suction. The residue was washed 3 x 50 mL of boiling de-ionised water and then with

acetone until no more colour was removed and suction applied until the fibre appeared dry. The fibre was then dried for 2 h at 105°C, cooled to room temperature in a desiccator and weighed.

The percentage NDF were calculated from the equation:

°/ NDF = 100 x dry wt. correction factor x [ (wt. sinter + fibre) - (wt. sinter) ] / sample wt. -24/27

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For lignin determination the reagent used was 720 mL concentrated sulphuric acid diluted with 540 mL de-ionised water to 72% (w/v). The sinter was half filled with cooled (15°C) H₂SO₄ reagent and stirred to a smooth paste with a glass rod and the liquid level maintained by refilling with H₂SO₄ as it drained away. After 3 h the acid was filtered off under vacuum and the contents washed with hot water and acetone until the residue was free of acid reagent. This was followed drying the sinter at 105°C for 2 h, cooling it off in a desiccator and weighing it. It was then ignited at 550°C, cooled in a desiccator and re-weighed. The percentage lignin was then calculated from the equation:

₀/ 1 _jrιn:_n_(100χdry wt. correction factor)χ[(wt. sinter + lignin + ash)-(wt. sinter + ash)]/ /oLlyi lli l— 'sample wt.

The %cellulose was determined by subtracting the %lignin from the %NDF.

Microbial analysis

The amount of living aerobic colony forming units were quantified by plate counts, as the number of colony forming units (CFU) present per 1 g sample that developed in 48 h. The samples were incubated at 25°C on Chromocult agar. The presence of E. coli and Salmonella was determined by an independent laboratory using methods prescribed by the British Standards Institution (1998). -23/27

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Statistical analysis of data

The data in this study was analysed by using the SigmaStat^® computer

software package and all values presented as the mean ± SD (standard deviation). The probability levels used for statistical significance were P < 0.05 and parametric or non-parametric tests were used to compare different treatment groups.

Results and discussion

The temperature profiles during the composting phase (first 28 days) of the different treatments are presented in Figure 3.1. In none of the treatments did the temperatures rise above 33°C, which do not meet with the EPAs

(Environmental Protection Agency) PFRP (Process to Further Reduce

Pathogens) requirement, contained in US-EPA 40 CFR Part 503 (Hay, 1996).

Although temperature evolution is an indicator of microbial activity (Jimenez and Garcia, 1991 ), the lowered temperatures observed could have been a result of the high moisture content (70%) of the material and not a shortage of micro-organisms. It is therefore possible that higher temperatures could be reached if the initial moisture content of the material was lower at the time of loading. Low temperatures can on the other hand help to conserve N in composted materials, since high temperatures can cause high losses of N in the form of NH₃ during the early stages of composting (Sanchez-Mondero et al., 2001 ). -22/27

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In light of the low temperatures and the EPA requirements it was decided to do an analysis for total conforms, E. coli and Salmonella spp. in the end- products. The presence of coliform bacteria is often used as an indicator of the overall sanitary quality of soil and water environments and is simple to detect (Hassen et al., 2001). E. coli is the most representative bacterium in the group of faecal conforms (Le Minor, 1984) and can therefore be used as an indicator to the presence of faecal coliforms. The presence of Salmonella is considered as a major problem of the hygienic quality of compost (Hay, 1996) in the light of the diseases that might arise from contamination.

No E. coli or Salmonella was detected in any of the products, which means that the end-products in this study should be safe for general distribution. The total number of coliforms ranged between 2430 and 2903 CFU g^"1.

The percentage CO₂ and O₂ levels in air are shown in Figures 3.2 and 3.3, with the most activity observed during the first 8 days. This corresponded with the rise in temperature observed, which is the norm during the usual composting process (Tuomela et al., 2000). The nutrient parameters (TOC, P[totai], P-Bray 1 , NH , NO₂ and NO₃) of the different treatments at the time of loading are presented in Table 3.1 and at the time of loading, no significant

(P > 0.05) differences were observed for the measured parameters between the treatments containing SS. The mean percentage change of these parameters after composting and vermicomposting are presented in Table -21/27

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3.2. There was no significant (P > 0.05) difference in the mean percentage change of TOC in the different groups. This could be due to the fact that temperatures in the treatments did not go higher than 33°C and C lost in the form of C0₂ from the systems were minimal.

All the treatments containing SS showed a significant increase in total P ranging from 78.60 - >100%. Although all the treatments showed an

increase in P-Bray 1 values, it was only in the SS+WC and SS+WC+EM groups that this increase was statistically significant (P < 0.05). Ghosh et al. (1999) found that vermicomposted organic wastes released higher amounts of P-Bray 1. They ascribed this to the fact that earthworms take up P as a nutrient in their bodies for syntheses and release the remaining P in a mineralised form and concluded that vermicomposting might be an effective method producing better P nutrition from organic wastes. This is, in contrast with other studies where soluble P decreased after composting (Vuorinen and Saharinen, 1997) and vermicomposting (Ndegwa and Thompson, 2001 ).

N concentration in composted waste materials is one of the most important factors to study in ascertaining their agronomical value and NH₄ and NO₃ are the most interesting, since it can be assimilated directly by the root systems of plants (Sanchez-Mondero et al., 2001). NH in all the treatments containing SS showed a significant (P < 0.05) decrease ranging from 92.57 -

>100%, whereas the WC treatment showed an increase of more than 100% -20/27

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with an actual end value of 1.77±0.80 mmol L^"1. The levels of NO₂ showed a significant (P < 0.05) increase in all of the treatments containing SS and no significant (P > 0.05) change was observed in the WC treatment. According to Sanchez-Mondero et al. (2001) the presence of NO₂ in composted material is a clear indication of anaerobic conditions during composting. This could be due to the high moisture content of the material, which caused the development of anaerobic microenvironments. All the treatment groups showed a significant (P < 0.05) increase in NO₃, in excess of 100%. This can be explained by the fact that during composting the evolution of nitrogenous compounds is as follow:

2NH₄ ⁺ + 3O₂ → NO₂ ^" + 4H⁺ + 2H₂O (Nitrosomonas spp.)

2NO₂ ^" + 0₂ → 2NO₃ ^" (Nitrobacter spp.)

There were, however, differences between the different treatments with the following ranges of significance (P < 0.05); SS+WC+e/w and SS+WC+EM+e/w > SS+WC and SS+WC+EM > WC.

At the end of the study, the NO₃ concentration was higher than that of the NH₄, which is an indication that the right composting process had been followed (Finstein and Miller, 1985). Furthermore, the NH₄:NO₃ ratios (Table 3.2) were lower than 0.16, which is an indication of the maturity of the compost (Zucconi and de Bertoldi, 1987), in all the treatments ranging from -19/27

35

0.011-0.0016, except in the WC treatment (0.27). There were no significant

(P > 0.05) differences between the ratios in the treatments containing SS, indicating that there is no difference in the evolution of nitrogenous products between composting, micro-organism inoculation and vermicomposting.

The physical parameters (TS, VS, Ash, % NDF, % lignin and % cellulose) and pH of the different treatments at the start of the experiment are shown in Table 3.3, with no significant (P > 0.05) differences observed in the parameters between the different groups. The mean percentage changes in these parameters after completion of composting and vermicomposting are presented in Table 3.4, with no significant (P > 0.05) changes observed in the WC treatment. After 112 days of composting and vermicomposting, the pH of the WC showed an decrease of 5.75% (P > 0.05), while those in the treatments with sewage sludge showed an increase ranging between 13.67 and 26.47%, which were all statistically significant (P < 0.05). This follows the basic trend of pH during composting, where an initial decrease is observed due to the formation of organic acids, followed by an increase as a result of ammonium liberation (Tuomela et al., 2000). TS and ash contents showed an overall increase and the VS and the lignin an overall decrease, but it was only in the vermicomposted treatments that these changes were statistically significant (P < 0.05). -18/27

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According to Neuhauser et al., (1988) an increase in ash contents and a decrease in VS are an indication of stabilisation of composted materials. The increase in TS could be due to the fact that the material that was vermicomposted were physically broken down and therefore had an increased density, as well as the fact that the moisture content (as a function of TS) of the material was significantly lower. It was also observed that the material showed a volume reduction, although this was not quantified. This volume reduction and decrease in moisture content relates into a reduction of handling and transport costs.

The %NDF and %cellulose decreased significantly (P < 0.05) in all the treatments containing SS, with no significant (P > 0.05) difference between the different treatments. Cellulose degradation is correlated with microbial biomass (Entry and Bachman, 1995) and can also be utilised by epigeic earthworms as a direct food source (Zhang et al., 2000). The gut passages of earthworms do, however, reduce soil microbial biomass (Zhang et al., 2000), which might explain why the breakdown of cellulose in the treatments without earthworms were fractionally higher, although not statistically significant (P > 0.05). A significant (P < 0.05) decrease in the % lignin was only observed in the two treatments that were vermicomposted. This could be due to the fact that lignin degradation is regulated by the thickness of the material (Tuomela et al., 2000) and that earthworms eat, grind and digests organic wastes, converting it to much finer materials (Aranda et al., 1999). -17/27

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Entry and Bachman (1995) also concluded that cellulose, but not lignin degradation, was correlated with microbial biomass, while Faure and Deschamps (1991 ) found that inoculating organic wastes with cellulolytic and ligninolytic bacteria had no effect on degradation. Further, material with high lignin content can be consumed by earthworms, resulting in sustained population sizes (Senpati et al., 1999).

The results of the particle size analysis are given in Table 3.5 and are expressed as the geometric mean size and the geometric standard deviation, as well as the percentage change. The vermicomposted treatments with the EM inoculate had the highest reduction in particle size followed by the vermicomposted treatment with no inoculate. These two groups also showed less heterogeneity, expressed by the higher geometric standard deviations observed. This could be due to the presence of biologically inactive material, e.g. plastics (by-products of the explosives used in mining) present in the wood chips.

It can be therefore be concluded that vermicomposting industrially produced wood chips and sewage sludge are superior to those merely composted, in the light of TS and VS reduction and the increase in ash contents. It was also shown that only the vermicomposted treatments showed significant -16/27

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reductions in lignin and that the addition of a microbial inoculate did not increase the rate of decomposition.

EXAMPLE 4

This example makes reference to the following enclosed drawing wherein:

Figure 4 depicts a graph of mean bodyweight (g) ±SD of earthworms (E. fetida) over 84 days (n=150). *Significantly different (P < 0.05).

(SS - sewage sludge; WC - woodchips; EM - micro-organism inoculate).

Materials and Methods

Air-dried samples of wood chips (WC) and sewage sludge (SS) were again obtained from platinum mines.

The earthworm (e/w) species E. fetida ("tiger worm") was again used. A commercial preparation of micro-organisms (EM™) were used in the

inoculation experiments which primarily consisted Pseudomonas,

Lactobacillus and Saccharomyces spp. -15/27

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Substrates utilised

A mixture of WC and SS with a mixing ratio of 3:1 (dry weight kg^"1) was used. The dry ingredients were mixed and moistened with distilled water to a 70% (by weight) moisture content. Two treatment groups with three replicates each were investigated and consisted of WC+SS and WC+SS+EM mixtures.

The substrate was put into plastic worm bins (60x40x30cm), placed in an environmental chamber (25°C) and composted for a period of 28 days. 100 mature worms were introduced after the 28-day composting period. This was done to avoid exposure of worms to the possible high temperatures during the initial thermophillic phase of composting.

Growth and reproductive success

Every 14 days for a period of 94 days, after the 28-day composting period, the earthworm biomasses were determined and moisture content of the substrates monitored. Biomass was determined by removing 50 worms from each container, washing them in distilled water and drying them on paper towels. They were then weighed in a waterfilled weighing boat using a Sartorius balance. This was done to prevent the worms desiccating and hence affect the weight of the earthworms.

Cocoon viability was determined by randomly harvesting 72 cocoons from each container and placing them in multidishes filled with distilled water. The water in these dishes was changed every third day to prevent bacterial -14/27

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growth, which could impact negatively on the results. The number of hatched cocoons and hatchlings per cocoon were recorded over a period of four weeks.

Heavy metal analysis

Prior to the experiment and at termination, nine earthworms per group were removed from the substrate. Afterwards these worms were placed on wet filter paper in Petri dishes for a period of 24 h to allow the depuration of their gut contents. This was done to prevent misleading results concerning the actual heavy metal content in the body tissues as a result of heavy metals present in the gut contents. After this 24 h period the worms were washed in distilled water, dried on paper towels and killed by freezing. They were individually weighed and frozen (-74°C) in polytop vials for heavy metal

analysis at a later stage. Samples of the substrate were also removed, placed in plastic bags and refrigerated until heavy metal analysis. Worms and compost samples were digested as described by Katz & Jennis (1983). Samples were individually dried and grounded, whereafter they were ashed at 550°C. Afterwards they were individually placed in test tubes and 10 mL of 55% nitric acid (HNO₃) was added. It was left overnight at room temperature to start the digestion process. The following day the samples were heated to 40 - 60°C for two hours and then 120 - 130°C for an hour, after which it was left to cool. 1 mL of 70% perchloric acid (HCIO) was added and this mixture was reheated to 120 - 130°C for an hour. The samples were -13/27

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allowed to cool before 5 mL of distilled water was added. Samples were then reheated to 120 - 130°C until white fumes were emitted. The samples were allowed to cool finally before they were microfiltrated.

The solutions were filtered through Whatman no. 6 filter paper into 20 cm³ volumetric flasks using Sartorius microfilter-holders and plastic syringes. Distilled water was used to make up a 20 cm³ filtered solution. These 20 cm³ solutions were microflltered through 0.45 μm Sartorius Cellulose Nitrate filter paper into polyvinyl containers and analysed by inductive coupled plasma spectroscopy (ICP-AES) for the different metals.

Statistical analysis of data

The data in this study was analysed by using the SigmaStat^® computer

software package and all values presented as the mean ± SD (standard deviation). The probability levels used for statistical significance were P <

0.05 and parametric or non-parametric tests were used to compare groups.

Results

At no stage during the study were any mortality observed and the mean biomass changes of E. fetida are presented in Figure 4. Before introduction into the mixture treatments, the mean biomass of earthworms in the SS+WC treatment was 0.44±0.01 g and 0.43±0.02 g in the SS+WC+EM treatment. There was no significant difference (P > 0.05) between these two values. On day 14 the mean biomass of the earthworms reached a maximum value of -12/27

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0.81 ±0.02 g and 0.77±0.02 g in the SS+WC and SS+WC+EM groups respectively, which was both significantly (P < 0.05) higher than the initial biomass. From day 14 to 84 the mean biomass decreased to 0.49±0.03 g in the SS+WC and 0.51 ±0.01 g in the SS+WC+EM, with a significant difference (P < 0.05) between the two values. These values were both significantly (P <

0.05) higher than the initial biomass.

The mean hatching success of cocoons produced in the SS+WC group was 46.8±2.4% (n=216) and significantly lower than the 68.0±2.8% (n=216) in the SS+WC+EM group. The mean number of hatchlings per cocoon was

2.7±0.1 for the SS+WC and 3.0±0.2 for SS+WC+EM group, with no significant difference (P > 0.05) between the two values.

The heavy metal content in the two substrate mixtures for Al, As, Cu and Ni are summarised in Table 4.1 and it was found that there were no significant differences (P > 0.05) for the selected metals. The initial and final body burdens of heavy metals present in the earthworm tissues are presented in Table 4.2. Initially there was no statistical difference (P > 0.05) between the heavy metal concentrations in the body tissues of the earthworms in the two groups. After termination of the experiment the heavy metal content of earthworms in the SS+WC was significantly higher (P < 0.05) than at the start for all the heavy metals measured, except As, which was below the detection limit of 0.05 μg.g^"1. In the earthworms exposed to SS+WC+EM, the -11/27

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heavy metal showed no significant changes (P > 0.05) after 84 days. The bioconcentration factors (BCF) for the different heavy metals in the earthworm body tissues after the 84-day vermicomposting period are shown in Table 4.3. It is evident that the BCFs of earthworms in the SS+WC group was almost double that in the SS+WC+EM groups for Al, Cu and Ni.

Discussion

From the results (Figure 4 and Tables 4.1 to 4.3) it is evident that the earthworms in both treatment groups were exposed to a mixture of contaminants, amongst others Al, Cu and Ni. This makes it difficult in assessing the effects of toxicants since the actual risks towards organisms are determined by the availability of these toxicants. The effects of Cu (Spurgeon and Hopkin, 1995; Van Gestel et al., 1991 ) and Ni (Lock and Janssen, 2002; Scott-Fordsmand et al., 1998) on growth and reproduction are well documented, but little or no information on Al is currently available.

In addition there is a lack in literature on the effects of these metals, as mixtures, towards E. fetida. With reference to the hazards these metals might pose to use in rehabilitation programmes, Al, Cu and Ni are all higher than the ranges proposed by the DWAF (1996) for agricultural use. This should be taken into account when choosing plant species to be used in rehabilitation, as well as monitoring the amounts of these metals leaching into groundwater. -10/27

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The data on growth compares well with previous studies where it was found that E. fetida reached a mean biomass of ±0.45 g under optimum conditions (Reinecke et al., 1992). The fact that the mean biomass of worms exposed to SS+WC were significantly lower (P < 0.05) than those exposed to SS+WC+EM, could be a direct cause of the bioavailability of the heavy metals in these substrates. Both the groups, however, showed a decrease in biomass after day 14 (Figure 4), which might be attributed to the presence of the elevated heavy metal concentrations. Growth can therefor be considered as a sensitive parameter in assessing the effects of Al, Cu and Ni towards E. fetida. This is in agreement with the findings of previous studies on the effects of Cu in the form of CUNO₃ on growth (Reinecke and Reinecke, 1996) who found that growth of E. fetida was negatively affected at substrate concentrations of 200 μg.g^"1.

Regarding growth as endpoint it can therefore be concluded that vermicomposting wood chips and sewage sludge utilising E. fetida are economically viable. In view of the fact that that the earthworms in the mixture containing the micro-organism inoculate performed better, with mean biomass as endpoint, it is anticipated it might yield better results on large- scale vermicomposting technologies.

The mean hatching success, which can be considered as an endpoint for reproductive success, was significantly higher (P < 0.05) in the SS+WC+EM -9/27

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group than in the SS+WC group, although there was no difference (P > 0.05) in the mean number of hatchlings between them.

Venter and Reinecke (1988) concluded that the mean hatching success of cocoons produced by E. fetida was 73% and that each cocoon produced a mean of 2.7 hatchlings. The hatching success of 68%, produced by worms in the SS+WC+EM mixture, compared favourably to the 73% as established by Venter and Reinecke (1988), while the hatching success of cocoons from the SS+WC mixture was much lower at 45%. The data referring to hatching success in the SS+WC substrate, with a high Ni (551 μg.g^"1) and Cu (315 μg.g^"1) concentrations of, is in concordance with the results of previous authors. Lock and Janssen (2002) reported that the EC₅o of Ni, based on cocoon production, at 362 μg.g^"1 and Spurgeon and Hopkin (1995) found that earthworm reproduction was significantly reduced in copper contaminated soils. Reinecke and Reinecke (1996) found that no cocoons were produced by E. fetida exposed to Cu concentrations of 200 μg.g^"1. Hatching success is therefore a much more sensitive parameter than growth when assessing the potential of utilising E. fetida in vermicomposting wood chips and sewage sludge.

The fact that hatching success in the group inoculated with micro-organisms were higher could possibly be ascribed to the fact that the Ni and Cu, which have detrimental effects on reproductive success, were less available to -8/27

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earthworms. Micro-organisms are capable of actively (bioaccumulation) and passively (biosorption) concentrating metals (Unz and Shuttleworth, 1996). It has experimentally been shown that Saccharomyces (Simmons et al., 1995) and Pseudomonas (Churchill et al., 1995), both of which were present in the inoculate, exhibit wide variation in the biosorption of metals. This could present a possible explanation for the disparities observed between the growth and reproductive success data observed between the two groups. This fact can be verified by the body burden of heavy metals observed in the earthworms body tissues, where the worms in the substrate containing an inoculate, had significantly lower (P < 0.05) levels of Al, Cu and Ni, which also reflected by the calculated BCF's.

Conclusions

It can be concluded that the growth of E. fetida was not inhibited when utilised as vermicomposting species of industrially produced wood chips and sewage sludge or the addition of a micro-organism inoculate. Reproductive success of earthworms in the SS+WC treatment groups decreased and bioconcentrated Al, Cu and Ni in their body tissues. Earthworms in the treatment group with the addition of a micro-organism inoculation, on the contrary, did not bioconcentrate any heavy metals in their body tissues and had a significantly higher reproductive success than their counterparts in the treatment without the micro-organism inoculation. This indicated that the micro-organisms present in the inoculate rendered the heavy metals present -7/27

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in the wood chip and sewage sludge mixtures unavailable through either biosorption of bioaccumulation.

It therefore seems that the most economically feasible way to bioconvert wood chips and sewage sludge utilising E. fetida, would be with the addition of a micro-organism inoculate.

EXAMPLE 5

This example makes reference to the following enclosed drawing wherein:

Figure 5 is a perspective view of a windrow for the composting and vermicomposting of a medium for treating tailings bodies of mining activities, in accordance with the invention.

From pilot studies it was concluded that for the successful composting of wood chips (WC) and sewage sludge (SS), a mixing ratio of 3:1 is required, with the composting/vermicomposting process extending over a period of 4-6 months.

To commercialise the method according to the present invention, the first step is to compost the WC and SS mixture for a period of 30 days by -6/27

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constructing windrows, an example of which is shown in figure 5. Thereafter the material is covered with netting (to prevent predation by birds) and vermicomposted using earthworms (Eisenia fetida) for a period of 4-5

months at a rate of 25 g of worms per kg of material.

Optimum dimensions for constructing windrows were found to be 2 tons of composting mixture per meter length, with a height of 1 m and a width of 2m as shown in Figure 5. This implies the use of 50 kg of earthworms per windrow.

The composted and vermicomposted medium that is obtained is then mixed into the tailings as described above in Examples 1 and 2.

It was found that the composted and vermicomposted medium according to the invention provided a favourable alternative and/or addition to the use of topsoil for soil amendment and, subsequently, waste wood chips and sewage sludge, which are major sources of organic carbon and nitrogen are viable sources of essential nutrients and organic matter when bioconverted in accordance with the present invention. Wood chips are further beneficial as an organic ameliorant during revegetation and the primary reason for incorporating wood chips as ameliorate is to improve the cation exchange capacity, thereby lowering the base saturation and improving the ability of the slime to adsorb excess salts. Wood chips also ameliorate the physical -5/27

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properties of the growth medium by increasing the water holding capacity. Organic material also stimulates biological activity, which is essential for nutrient recycling.

A further advantage of this method is that wastes produced from the mines, such as slimes, wood chips and sewage, are being used to rehabilitate the tailings and to decrease soil, groundwater and air pollution.

It will be appreciated that variations in detail are possible with a medium and method according to the invention for treating tailings of mining activities without departing from the scope of the appended claims.

Claims

-4/2750CLAIMS

1. A method of treating a tailing body of mining activities including the step of applying wood particles to the tailing body.

2. A method according to claim 1 wherein the wood particles are wood chips recovered from waste timber which is a by-product of mining activities.

3. A method according to claim 2 wherein the wood chips are in the form of timber mine props disintegrated in blasting operations.

4. A method according to any one of the preceding claims wherein the wood particles are pre-treated with an acid.

5. A method according to claim 4 wherein the acid is nitric acid (HNO₃).

6. A method according to any one of the preceding claims wherein the wood particles are applied to a top surface of the tailing body.

7. A method according to claim 6 wherein the particles are applied in the form of a coating. -3/27

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8. A method according to any one of claims 1 to 5 wherein the particles are worked into the tailing body.

9. A method according to claim 8 wherein the particles are dug into the body.

10. A method according to claim 8 or claim 9 wherein the particles are worked into the body to a level of about 30 cm below an outer surface of the body.

11. A method according to any one of the preceding claims wherein the particles are applied to an existing tailing body in the form of a dam to rehabilitate the dam.

12. A method according to any one of claims 1 to 10 wherein the particles are intermittently applied to the tailing body during the development thereof.

13. A method according to any one of the preceding claims wherein the wood particles are applied at a rate of between 60 to 90 tons per hectare of tailing dam surface. -2/27

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14. A method according to any one of the preceding claims which includes the step of composting the wood particles prior to the step of applying the particles to the body.

15. A method according to claim 14 wherein the step of composting the wood particles includes the step of vermicomposting the particles.

16. A method according to claim 15 wherein the step of composting the wood particles further includes the step of mixing the particles with another source of organic material.

17. A method according to claim 16 wherein the other source of organic material comprises sewage.

18. A method according to claim 17 wherein the wood particles and sewage are mixed and allowed to form compost, after which the compost is inoculated with worms and allowed to form a vermicomposted medium.

19. A method according to claim 18 wherein the worms are from the species Eisenia fetida. -1/27

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20. A method according to claim 18 or claim 19 wherein the wood particles and the sewage are mixed in a ratio of between 3:1 and 3:2.

21. A method according to any one of the preceding claims, which includes the step of planting selected plants on the treated tailing body.

22. A method according to claim 21 wherein the plants are selcted from the group consisting of Cenchrus ciliaris variety Molopo; Cenchrus ciliaris variety Gayndah; Eragrostis lehmanniana (Lehmann's Love

Grass); and Eragrostis curvula) and mixtures thereof.

23. A method of treating a tailing body of mining activities substantially as herein described and exemplified.

24. A tailing body treated according to the method of any one of claims 1 to 23.

25. A medium for the treatment of tailings bodies of mining activities comprising a mixture of wood particles and another source of organic material, which has been composted. 0/27

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26. A medium according to claim 25 wherein the wood particles are wood chips recovered from waste timber which is a by-product of mining activities.

27. A medium according to claim 25 or 26 wherein the wood particles are in the form of timber mine props disintegrated in blasting operations.

28. A medium according to any one of claims 25 to 27 wherein the other source of organic material is in the form of sewage.

29. A medium according to any one of the preceding claims wherein the mixture is further vermicomposted.

30. A medium according to any one of claims 25 to 29 which further includes a selection of micro-organisms.

31. A medium for the treatment of tailings bodies of mining activities substantially as herein described and exemplified.