CN1585677A - 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

Media and method for treating tailings after mining activities

Introduction and background

The present invention relates to a medium and a method for treating mining active tailings (tailings).

Human activities such as mining generate large amounts of waste that pose economic and environmental problems. This is because not only does the treatment of these wastes require expensive large areas of land, but the wastes also contaminate the soil, ground water and air. In particular, the mining of platinum, gold and other minerals has considerable environmental impact due to the creation of large tailing dams (tailing dams). Tailings are produced as a slime waste stream during mineral processing and are essentially biologically non-growing media with limited water holding capacity and high percentage of alkali saturation. In addition, tailings also contain high concentrations of potentially environmentally toxic heavy metals that can leach into groundwater.

The Walmsley (1987) study showed that although the tailings are not saline, they contain high concentrations of manganese, iron and sulphur, which are phytotoxic at high concentrations. For example, platinum tailings consist primarily of sand (75%) and silt (20%), with the remaining 5% of the particles being clay and negligible organic components. The above factors complicate the proper vegetation restoration of the tailings to achieve the pre-mining land application potential and lead to environmental degradation of the area. In addition to inorganic tailings, the mining of platinum further produces large amounts of organic waste, namely eucalyptus willow (Saligna folium alpiniae oxyphyllae) wood chips and sewage sludge. The tailing dam poses a series of environmental hazards including air, dust and groundwater pollution due to its physical and chemical properties, while the dumped wood chips add to the risk of fire during the hot, dry summer months.

The wood chips generated upon extraction of platinum originate from the explosion of underground complete wood pillars. The result is that the wood chips and ore are processed together during the initial grinding and extraction stages of mineral processing. The wood chip fraction is separated as a by-product by screening before the platinum is extracted. Due to the explosion, wood chips contain high concentrations of nitrates, which are already high enough to cause health problems when they penetrate into groundwater, such as methemoglobinemia (DWAF 1996). At present, wood chips are incinerated at high cost.

Thus, slime, wood chips and sewage pose ecological and environmental liability to the mining industry.

The primary purpose of the tailings remediation program is to restore the site to its pre-contaminated condition, which often includes vegetation restoration to stabilize the treated soil. This is difficult and expensive due to the difficulty in obtaining topsoil and the lack of organic matter, elemental imbalances and the lack of essential nutrients in the tailings dam. In one attempt to address these problems, topsoil is either planted from other areas (which then need to be rehabilitated) or treated regularly with inorganic fertilizers, which is expensive and ecologically intolerable. Most residual mine dumps are currently reconstituted by growing grass on the dumps. However, promoting viable and sustainable vegetation is a problem due to the ineffectiveness and phytotoxicity of the growth medium.

U.S. patent No. 6,004,069 discloses a method of providing a protective cover of a subatmospheric inorganic composite on sulfide-containing tailings and sulfide-bearing mineral waste, the method comprising the steps of:

i) providing a deposit of sulphide particulate material comprising at least one of tailings comprising sulphide minerals, waste rocks having sulphides and mineral waste having sulphides, the sulphide particulate material having a low water conductivity (hydraulic conductivity), the deposit having an apex and a slope which encloses an angle of more than 0.5 degrees with the horizontal;

ii) depositing a first particulate layer comprising inert fine species having an average particle size of between 10Em and 200.mu.m and a water conductivity of greater than 10.sup. -7cm/sec and a matrix suction value of greater than 4cm of water on the deposit of sulphide particulate material, the first particulate layer being deposited such that the first particulate layer extends over the deposit of sulphide material to a depth of more than 4 cm;

iii) depositing a second particulate layer on the deposit of sulphide particulate material, the second particulate layer comprising inert fine particulate matter having an average particle size between 200.mu.m and 5000.mu.m, a hydraulic conductivity between 10.sup. -3 and 1cm/sec, the hydraulic conductivity of the second particulate layer being at least one order of magnitude higher than the hydraulic conductivity of the first particulate layer, and a matrix suction value, the ratio of the matrix suction value of the second particulate layer to the base mode suction value of the first particulate layer being less than 1: 2, the second particulate layer being deposited to provide for extension of the second particulate layer on the first particulate layer to a depth which is at least 1.5 times the matrix suction value of the second particulate layer measured in cm of water; and the combination of (a) and (b),

iv) depositing a third particulate layer comprising inert coarse particulate matter having an average particulate size greater than 3mm and a water conductivity greater than 1cm/sec on the sulfide particulate material deposit, the third particulate layer being deposited to provide the third particulate layer extending over the second particulate layer to a depth of more than 6 cm.

The inert fine material contained in the first particulate layer is selected from the group consisting of oxidized mill tailings, low sulfide containing mill tailings, desulfurized mill tailings, neutralized mill tailings, loess, fine sand, sandy clay, sandy loam, fly ash, sludge, tillite, alluvial source fine material, and mixtures thereof.

The inert fine particulate material contained in the second particulate layer is selected from the group consisting of granulated slag, granulated desulphurised slag, desulphurised rock, fine sand, fine crushed rock, winter sand and mixtures thereof.

The inert coarse particulate matter contained in the third particulate layer is selected from the group consisting of crushed rock, crushed stone, crushed limestone, pebbles and naturally occurring coarse materials, crushed destructive materials and mixtures thereof.

Some of the disadvantages of the above-described methods are that no organic substances are added to the top layer and that they are relatively complex and expensive due to the many different substances and steps involved. It is not commercially viable.

Object of the Invention

It is therefore an object of the present invention to provide a medium and a method for processing tailings with which the aforementioned problems and disadvantages are overcome or at least alleviated.

Summary of The Invention

According to a first aspect of the present invention there is provided a method of treating a residual ore body of a mining activity, the method including the step of applying wood particles to the residual ore body.

The wood particles may be wood chips recovered from waste wood and may be a by-product of mining activities, more particularly in the form of wood mine pillars that disintegrate in an explosion operation.

The wood chips may be pretreated with an acid.

The acid may be, for example, nitric acid (HNO)₃)。

The wood chips can be applied to the top layer of the ore body, for example in the form of a cover layer.

In a preferred form of the method, the wood chips are processed into the tailings bodies, such as by mechanically and/or manually digging the wood chips into the tailings bodies.

The wood chips are preferably processed into the tailings bodies at a level of about 30cm below the external surface of the tailings bodies.

The wood chips can be applied to the residual ore body existing in the form of a dam to restore the dam.

However, in a preferred form of the process, the chips are intermittently applied to the tailings dam during its development.

The wood chips are preferably applied at a rate of 60-90 tons per hectare of tailings dam surface.

Further according to the invention, the method comprises the further step of composting the wood chips before the step of applying the wood chips to the tailing bodies.

Yet further in accordance with the present invention, the step of composting the wood chips comprises the step of composting the wood chips into worms.

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

Other sources of organic material may include contaminated water,

wood chips and sewage may be mixed to enable the formation of compost, which may thereafter be inoculated with worms to enable the formation of a worm compost medium.

The worms may be from the species earthworm (Eisenia fetida).

If the availability of sewage is not a limiting factor, the wood chips and sewage can be mixed in a 3: 1 or 3: 2 ratio.

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

According to another aspect of the invention there is provided a composted medium for treating residual ore bodies of mining activities, the medium comprising a mixture of wood particles and another source of organic material.

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

The wood chips may be in the form of wood ore pillars that disintegrate in an explosion operation.

Other sources of organic material may be in the form of sewage.

The mixture can be further processed into vermicompost.

The medium further may include a selection of microorganisms.

The invention will now be further described by way of a number of embodiments, with reference to the accompanying drawings and figures. For clarity, the description of the drawings is set forth in the related embodiments.

Example 1

This embodiment refers to the following additional figures, wherein:

FIG. 1.1 is a flow chart of a method according to the invention; and

figure 1.2 is a final view of the dam showing grass growing on its sides to restore the tailings dam.

A mining method including a method of treating or restoring a mineral tailings dam according to the present invention is generally illustrated by the section and flow diagram in fig. 1.1.

The mineral may be, for example, platinum (Pt) ore 10. The mined products and waste, including wood particles in the form of wood chips or wood chips, are indicated at 12. Wood chips originate from well known wood mine props that disintegrate in the explosive operation of mining. The mixture is fed to a flotation stage 14 where the lighter waste wood is separated from the heavier platinum and slurry in a known manner.

The platinum and slurry at outlet 16 are also separated at 20 in a well known manner. The platinum is recovered at 22 and the remaining slurry is pumped to a remote location at 24 to form a tailings dam 26, again in a known manner.

The waste wood at the outlet 18 of the flotation stage 14 is ground and rolled at 28 to form wood chips 30.

It has been determined that known tailings dams contain unacceptably high concentrations of intractable elements that can leach out of the rain and into underground water sources, thereby contaminating those sources. The elemental composition of the chip sample and the tailing dam sample, respectively, is shown in table 1.1, and is water soluble and can be moved as described above and determined by well known extraction procedures.

The elemental composition of the mixture corresponding to that in table 1.1 is shown in table 1.2, where wood chips 30 are applied to the tailings dam 26 as shown in step 32 in fig. 1.1.

From the results of the analyses on the wood chips and the tailings, respectively, it is clear that the tailings contain high concentrations of major elements of calcium (Ca), magnesium (Mg), sodium (Na), Sulfate (SO)₄) And chlorine (Cl) concentration. High SO in tailings₄The concentration shows the ability to generate acid over time. This is due to the remaining low bicarbonate (HCO) in the sample₃) Concentration was confirmed, indicating that the buffer capacity in the tailings was almost exhausted. The need for increased adsorption capacity also passed a high base saturation of 21.48% and 2.09mS cm^-1High Electrical Conductivity (EC) indicating that those elements that are not currently bound will be carried by any rain water past the dam into the groundwater. As regards the trace elements, the concentrations of zinc (Zn) and manganese (Mn) and the potentially toxic heavy metals aluminium (Al), nickel (Ni), cobalt (Co) and arsenic (As) exceed the recommended standard values, and they are present in high concentrations in the tailings. In contrast, wood chips provide a means of adsorbing some of the excess elemental concentration despite the high Al concentration.

The negative surface charge of the chips is known to attract and bind certain elements and the results in table 1.2 clearly show that increasing the chip application rate decreases Ca, Mg, K, Na, SO₄And the concentration of Cl, Mn, Cu, Zn, Ni and Co. The reduction in the concentration of the above-mentioned elements in the extractable water fraction is also clearly reflected by the lower conductivity (EC) after the application of the increased volume of wood chips. Thus, as wood chip utilization increases, the concentration of elements potentially able to leach into the groundwater gradually decreases.

It has been found that 0.01% nitric acid (HNO) is used₃) Solution pretreatment of wood chips will result in lower wood chip applications with the same efficiency in reducing the concentration of potentially toxic elementsAnd (4) rate.

Likewise, as described in more detail in example 5 below, pre-composting wood chips (with or without sewage sludge) to worms may increase the bulk density of the material that must be applied to the tailings and reduce the time period for composting.

It has further been found that the use of 60-90 tons of wood chips per hectare of tailings dam surface produces good results.

With respect to fig. 1.2 showing the tailings dam 26, acid pretreated wood chips are processed into the tailings dam 26 at a level 34 of about 30cm below the tailings dam outer surface 36. The wood chips are preferably machined into the fixed side of the dam intermittently over a period of time as the dam is formed.

It is believed that the negative surface charge of the wood chips significantly increases the Cation Exchange Capacity (CEC), thereby reducing the movement of potentially toxic elements into the groundwater.

The tailings can be further recovered by sowing grass seeds on the above-mentioned side surfaces. It is anticipated that due to the nitrate levels present in the dam sides 38, including the wood chips, less or no inorganic fertilizer is required to promote the growth of the grass 40.

Example 2

This embodiment refers to the following additional figures, wherein:

FIG. 2.1 is a schematic design of the treatment and repetition of the method according to the invention on a platinum slime; and

FIG. 2.2 depicts the display of wood chip applications (0, 5, 15 and 30 tons ha)^-1) RDA biplot (biplot) of the relationship of nutrient availability to the growth medium. The species environmental dependence of the first axis was 0.749.

Design of experiments

The experimental site was constructed on a platinum ore tailings dam and monitored at 24X 4m for one and a half years²Small land blocks. The individual designs of the different treatment groups are summarized in fig. 2.1. The experiment consisted of 6 treatments on 3 replicate plots and 4 control plots.

Treatments 1 to 3

The first 3 treatments were combined according to standard practice with current vegetation restoration and fertiliser on mineralsApplications, but with increased wood chip applications (1: 5 ton ha treatment)^-1(ii) a And (3) treatment 2: 15 ton ha^-1(ii) a And (3) treatment: 30 ton ha^-1). The Zantate treated wood chips and untreated wood chips were applied in a 1: 1 ratio. The following fertilizers were applied in the first 3 treatments:

a) superphosphate 1200kg ha^-1

b)NH₄SO₄ 350kg ha^-1

c)KCl 400kg ha^-1

The first 3 treatments were vegetation reconstruction with a mixture of creeping and rootstocks of bermudagrass (Cynodon dactylon) and Cynodon nlemmuensis collected near the tailing dam. Bermuda grass and Cynodon nlemmuensis are planted in the same proportion at 6 rows per plot.

Treatment 4

No. 4 treatment with 30 tons ha^-1Wood chips and fertilizer applications as used in the previous 3 treatments were modified. The small land is composed of 10kg ha^-1Tribulus ciliate (Cenchrus ciliaris) (Molopo), 10kg ha^-1Is prepared from Tinospora Gagneria (Chloris gayana) and 5kg ha^-1The leaf of Oenothera sinuosa (Eragrostis curvula) (PUK E436) and 5kg ha^-1The seed mixture of Eragrostis lehmanniana was used for vegetation restoration.

Treatment 5

Treatment 5 with 30 t ha^-1Wood chips and fertilizer applications as used in previous treatments were improved. 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

30 tons ha for treatment 6^-1And (3) improving wood chips. Chemical analysis of the tailings (table 2.5) was used to determine the fertilization rate for optimal growth conditions. 800kg ha^-1Ammonium Monosulfate (MAP) fertilizer is used to improve the nutrient status of the growth medium. Plots were vegetated with a grass seed mix similar to that used in treatment 5 (table 2.1).

Materials and methods

Botanic measurements

The plants on the site are often used at 1m²Bridge point devices (bridge points) mounted on the frame monitor. Frequency of species and substantial coverage of species thus using 125 points m^-2And (4) determining. The standard grass biomass was then determined. Will be at 1m²The standard biomass established in the signal region (quadrant) was trimmed with wool scissors and sorted by species. The biomass was dried at 60 ℃ for 48 hours and weighed.

Soil sampling and analysis

Soil samples (about 500g) were collected with a soil punch. The 50 gram sub-samples were quantified for particle size distribution according to the procedure advocated by the American Society for Testing and Materials (1961). Soil samples were chemically analyzed by the 1: 2(v/v) extraction procedure described by Black (1965) to determine the water-soluble alkaline cationic components (Ca, Mg, K and Na) and trace elements (Fe, Mn, Cu and Zn) and heavy metals (As, Se, Al, Cr, Co, Ni, Pb and Cd).

Water-soluble basic cations (Ca, Mg, K and Na), trace elements (Fe, Mn, Cu, Zn) and heavy metals (As, Se, Al, Cr, Co, Ni, Pb and Cd) were quantified by atomic absorption spectroscopy using spectra.aa-250 (Varian, australia). Anion (F, Cl, NO)₃、PO₄And SO₄) Quantification was performed by ion chromatography (Metrohm 761, switzerland). 75ml of soil was used for 1: 2 extraction analysis. Ammonia (NH)₄) The concentration is quantified by the ammonia selective electrode method as described by Banwart et al (1972). Bicarbonate salts (HCO) in soil₃) The content of (D) was determined by potentiometric titration with an end point of standard 0.005M HCl solution, pH4.5 (Skougstd et al, 1979). Boron (B) concentrations were determined by the azomethine-H-method described by Barrett (1978) using a VEGA 400 spectroquant with absorbance colorimetry at 420 nm.

The pH and conductivity (EC) of the soil was determined in the 1: 2 extract at 25 ℃ using a WTW LF92 conductivity meter.

Plant, soil and water chemistry data STATISTICA ver.6 (Statsuf)t, inc.2001) were analyzed. The influence of the treatment and the wood chip concentration was investigated by redundancy analysis (ReDudancy analysis) (RDA) (Ter Bfaak and1997). RDA is a limited linear classification (ordering) method and thus is also a direct gradient analysis technique that integrates classification with regression (Ter Braak, 1994). An advantage of applying categorical ranking and direct gradient analysis as an analytical tool is that it can provide graphical results of the relationship between variables and related environmental factors. Screening criteria established by the U.S. Department of Energy (USA Department of Energy) (Efroymson et al, 1997) can be used as toxicology guidelines.

Results

Plant composition

Tables 2.2, 2.3 and 2.4 summarize the species frequency, basic coverage and biomass measured in 6 treated and control plots. During the measurement 14 grass species were encountered. The treatments with the highest abundance of species were treatments 5 and 6, which were seeded with the mixture of species shown in table 2.2. The seed mix used in treatment 4 produced the highest total basal coverage (5.2%). All other treatments, including controls, had very similar basal coverage (+ -3%). The total biomass between plots was not significantly different due to the high variation in standard biomass. The total biomass was highest in the plots treated with treatment 6. This is mainly due to the activity of Tribulus terrestris.

Tribulus ciliate variety Molopo is the most successful species established from seeds, based on frequency, basal coverage and biomass results. Other species which also performed satisfactorily were the Tribulus ciliate variety Gayndah (treatment 6), Eragrostis lehmanniana (Lehmann's LoveGrass) (treatments 4-5) and Saxatilis flexuosa (treatment 4). Surprisingly, a large crabgrass (Digitaria riantha) that generally performs very well in restored areas (Smuts FingerGrass) (Mentis 2000) cannot be established on experimental plots. One possible reason for the unsuccessful establishment of the crabgrass is the drying conditions at the beginning of the experiment.

Chemical properties of soil

3 samples were taken from the tailings for chemical quantification and to determine the fertilizer application of treatment 6 (table 2.5). Samples 2 and 3 are very similar chemically, but the nutrient concentration in sample 1 is considerably greater than in the first two samples. This shows a high variability in the chemical composition of the sample. The 1: 2 water extract (Table 2.5) further showed that heavy metal toxicity to plants could be a serious problem in the unmodified tailings. Plant growth can be affected As a result of increased soil solution concentrations of Pb, Cr, Co, Se, and in particular As (Efrotmson 1997).

The results of the 1: 2 water extract program shown in Table 2.6 show the concentration of elements in the soil solution that can be adsorbed by plants at 2 months in 2002. Generally, the concentrations of macroelements (Ca, Mg and K) are slightly lower than the preferred concentrations for effective growth. The available phosphates and nitrates in soil solutions have also been exhausted due to assimilation by plants. NO₃And PO₄Will be the limiting factor for plant growth.

In addition to Cu, no potential micronutrient toxicity occurs at the existing pH levels. Cu is as high asUp to 0.827 mu mol/dm³Is present at an elevated concentration (potential level of phytotoxicity according to Efroymson (1997) of 0.94. mu. mol/dm³)。

The pH of the growth medium remained alkaline (average pH of all treatments: 7.8. + -. 0.025). The low EC also confirms the low nutrient status of the growth medium and further shows that salinity is not relevant. The sodium adsorption ratio SAR is also lower than the recommended value of 1, indicating the absence of potential soil sodium (solubility).

By comparing table 2.5 and table 2.6 it is possible to determine the change in chemical properties of the tailings due to time, plant growth and application of wood chips. The concentration of all macroelements in the tailings is considerably reduced. The sulfate concentration remained relatively the same or slightly decreased in the control plot and the plot treated with the low concentration wood chips. In treatment 6, the sulphate concentration in the growth medium solution was also considerably reduced, which is comparable to the use of 30 tons ha^-1Other treatments of wood chip treatment are less typical than others. The concentrations of the trace elements Fe, Mn and Cu are increased to show the solubility of these elementsAnd (4) increasing. However, there is a decrease in zinc and boron concentrations. The pH of the soil solution remains relatively the same as about 7.8. The conductivity at the end of the study also dropped considerably from 2.267mS/cm (unmodified tailings) to 0.296 mS/cm.

To elucidate the effect of increasing wood chip application on the chemistry of the tailings, RDA was performed and the results are shown as a two-way graph of RDA of species (chemical variables) versus wood chip application as a factor (fig. 2.2). Since only one variable is examined, both the canonical axis (canonical axis) and the substance class classification alignment axis (organization axis) are represented on the first classification alignment axis. Chemical variables as species were 74.9% correlated with wood chip application as environmental factor. According to fig. 2.2, the most relevant chemical variables to the chip application gradient are B, P and Cu (positive correlation) and pH (negative correlation). The pH of the medium will acidify with increasing chip application and the concentration of B and especially Cu will increase. Because of the macronutrient concentration (Ca, Mg, K, Na, SO)₄) And Conductivity (EC) is weakly correlated with the first sorting axis, these variables are less affected by increased application of wood chips.

Fig. 2.7 shows the correlation matrix between soil chemical variables. The salinity of the growth medium is due in large part to sulfates and in particular calcium sulfate, potassium sulfate, and magnesium sulfate. Calcium, magnesium and potassium are also highly relevant. However sodium is better associated with chloride. Iron, manganese and copper are homogeneously interrelated. The only significant negative correlation is between iron and ammonium.

Conclusions and suggestions

From the vegetation reconstruction results, many species that are particularly useful in highly diverse mixtures cannot be established. The results show that a seed mixture of Tribulus ciliate, Eragrostis lehmanniana, Panicum paniculatum (Panicum maximum) and Gerberia pseudolaris is sufficient. Finger grass (eleusineecofacana) is the most successful pioneer species. A possible reason for poor performance of the Fidelian grassland species is the low seeding rate of 1-2 kg/ha. Seeds (mass-sown species) must be sown at a rate of not less than 5kg/ha to ensure successful establishment. Tillers and runners of bermudagrass and Cynodon nlemmuensis may also be planted in the intervals for erosion control. Use of bermuda grass in place of Cynodon nlemmfuensis is preferred because bermuda grass is indigenous to the area, more drought tolerant and can form more effective coverage. The results also show that the seed mix of treatment 4 was more successful than the seed mixes of treatments 5 and 6. In treatment 4, less species were applied, but the same results were obtained as for the seed mixtures used in treatments 5 and 6. Both seed mixes provided the same amount of coverage, while the basic coverage of treatment 4 was higher than that of treatments 5 and 6. Depending on the results, different seed mixtures should also not affect biomass production. Biomass is more affected by the establishment of a particular species (in this case tribulus ciliaris) than by the total composition of the seed mixture.

The chemical growth conditions of the tailings were considerably improved during the experiment. The greatest considerations regarding the soil nutrient status of the improved slime material are its low fertility and the potential for the presence of trace elements and heavy metal toxicity, especially copper, chromium, selenium and arsenic. Despite the potential for phytotoxicity, the vigor and strength of life of grasses appears to be satisfactory. If the chemical compositions before and after the tailings are compared, the tailings are easy to seep. This may be a considerable consideration with respect to groundwater contamination.

Improved plots are expected to have elevated NO due to the initial high nitrate concentration in tailings and wood chips₃Concentration, however, this is not the case. One possible explanation for this is NO₃High fluidity, which results in a large amount of NO₃Exudation and high rate of plant uptake, which explains the vigor of the plants (Mengel)&Kirby, 1987). A further explanation is that some inorganic nitrogen is fixed as organic nitrogen by soil microorganisms due to nitrogen fixation at high C/N ratio (Tainton 2000).

Example 3

This embodiment refers to the following additional figures, wherein:

figure 3.1 depicts the temperature (° c) profile of the composting and worm composting system during the first 28 days. SS, sewage sludge; WC, wood chips; EM, microbial inoculation; e/w, earthworms;

FIG. 3.2CO describing composting and vermicomposting System in the first 28 days₂(%) graph. SS, sewage sludge; WC, wood chips; EM, microbial inoculation; e/w, earthworms; and

FIG. 3.3 depicts O of composting and Worm composting System during the previous 28 days₂(%) graph. SS, sewage sludge; WC, wood chips; EM, microbial inoculation; e/w, earthworm.

Materials and methods

Inoculation of organic waste, earthworms and microorganisms

Samples of air-dried Wood Chips (WC) and Sewage Sludge (SS) were obtained from platinum ore. The earthworm (e/w) species used were earthworms (Eisenia fetida) ("cutworm") which are earth-surface type and potential waste composting worms (Edwards and Bohlen, 1996). The breeding stock of earthworms (Eisenia fetida) used in this study was maintained on livestock manure at a temperature of + -25 ℃. Only mature zonal worms were used for the purposes of this study. A commercial microbial preparation (EMTM) was used for the inoculation experiments, which consisted mainly of Pseudomonas, Lactobacillus and Saccharomyces species.

Compost and vermicompost experiments

The application of a mixing ratio of 3: 1 (dry weight kg)^-1) WC and SS mixture of (a). The dry ingredients were mixed and humidified with distilled water to a moisture content of 70% (by weight). A study was conducted on 5 treatment groups with 3 replicates, consisting of WC + SS, WC + SS + EM, WC + SS + e/w, WC + SS + EM + e/w and WC mixtures. The substrate was placed in a plastic box (60X 40X 30cm), placed in an environmental chamber (25 ℃) and composted for 28 days. Treatment with earthwormsIn the middle, 100 mature earthworms were introduced after a 28 day composting period to avoid exposing the earthworms to the high temperatures possible during the initial thermophilic phase of composting.

Physical and chemical parameters

From day 0 (referring to the time of initial mixing of the waste before decomposition) to day 28, CO₂And O₂And portable CO for temperature₂And O₂Analyzer (Gas Data PCO)₂) And (6) measuring. As long as CO is present₂Increase or O₂Decreasing beyond the level in the air, the ventilation is manually increased to reverse the trend.

At the beginning and end of the experiment, the Total Solids (TS), Volatile Solids (VS), ash content, particle size distribution, NH were determined₄ ⁺、NO₃ ^-、NO₂ ^-pH, total and soil available P (P-Bray 1), Total Organic Carbon (TOC),% lignin and% cellulose.

TS was determined as a residue dried at 80 ℃ for 23 hours, and VS was determined by graying the dried sample at 550 ℃ for 8.5 hours (APHA et al, 1989). The particle size distribution was determined by sieving 100g of the material through sieves having mesh openings of 4.75, 4.00, 2.00 and 1.00mm, respectively. Particle sizes are reported as geometric mean and geometric standard deviation as described by Ndegwa and Thompson (2001).

Anionic NO₃ ^-、NO₂ ^-Determined by Capillary Electrophoresis (Waters Quanta 4000, Capillary Electrophoresis System, Waters, Mass.) as described by Heckenberg et al (1989). NH (NH)₄ ⁺The concentration is quantified by the ammonia selective electrode method as described by Banwart et al (1972). The pH of the substrate was determined in the 1: 2 extract at 25 ℃ after an equilibration period of 12 hours with intermittent agitation using a calibrated pH meter (Radiometer PHM 80, Copenhagen).

P_{[ Total]}The concentration was determined colorimetrically by the vanadium molybdate (vanadomolybdate) method. This required pipetting 200mL of the digested sample solution into a 50-mL volumetric flask, adding 10mL of vanadium molybdate reagent to the flask and diluting the volume with deionized water and mixing. After 10 minutes, the concentration was read on a colorimetric Continuous Flow Analysis System (Continuous Flow Analysis System, Squalar, the Netherlands).

TOC was determined by a separate laboratory using the Walkley-Black method (Walkley and Black, 1934), while P-Bray 1 was determined using Bray extractant number 1 (Bray and Kurtz, 1945).

% NDF,% lignin and% cellulose

% NDF (neutral detergent fiber, i.e. insoluble component of plant cells),% woodThe lignin and% cellulose were determined according to Rowland and Roberts (1999). For NDF determination, samples were air dried and milled (< 1 mm). The percent dry material was determined by drying the air dried sample at 105 ℃ for 3 hours and determining the dry weight correction factor; namely, it is¹⁰⁰/_{% of dried substance}。

The reagent consists of 18.61g EDTA and 6.81g Na dissolved in 500mL deionized water₂B₄O₇10H₂O, then 30g of Sodium Lauryl Sulfate (SLS) and 10mL of 2-etoxyethaneol are added. 4.56g of anhydrous Na₂HPO₄Dissolved in water alone, mixed with other solutions and finally diluted to 1000 mL.

0.5g of the air-dried material was placed in 250-mL, Erlenmeyer flask and 100mL of neutral detergent reagent was added. The solution was boiled and boiled for 1 hour. While still hot, the solution was filtered through a pre-weighed sinter (No. 2) while gentle suction was applied. The residue was washed with 3X 50mL boiling deionized water and then acetone until no more color was removed while applying suction until the fibers appeared dry. The fibers were then dried at 105 ℃ for 2 hours, cooled to room temperature in a desiccator and weighed.

The percent NDF is calculated from the following equation:

％NDF＝^{100 dry weight correction factor X [ (sinter + weight of fiber) - (sinter weight)]}/_{Sample weight}

For lignin determination, the reagent used was 720mL diluted with 540mL deionized water to 72% (w/v) concentrated sulfuric acid. The sinter is treated with cooled (15 ℃ C.) H₂SO₄The reagent is half-filled and stirred with a glass rod into a smooth paste and when it dries is filled H by refilling₂SO₄While maintaining the liquid level. After 3 hours the acid was filtered off in vacuo and the contents were washed with hot water and acetone until the residue was free of acid reagent. The sinter was subsequently dried at 105 ℃ for 2 hours, cooled in a desiccator and reweighed. It was then ignited at 550 ℃, cooled in a desiccator and weighed again. The percent lignin is then calculated from the following equation:

% lignin ═ lignin^{(100X Dry weight correction factor)) X [ (weight of sinter + Lignin + Ash) - (weight of sinter + Ash)]}/_{Sample weight}

% cellulose is determined by subtracting% lignin from% NDF.

Microbiological analysis

The amount of viable aerobic colony-forming units was quantified by plate count as the number of colony-forming units (CFU) present in each 1g of sample developed in 48 hours. The samples were inoculated on Chromocult agar at 25 ℃. Coli (e.coli) and Salmonella (Salmonella) were determined by the method specified by the british standard institute (british standards institute) (1998) for independent laboratories.

Statistical analysis of data

SigmaStat was used as data in this study^®Computer software package analysis was performed and all values are expressed as mean ± SD (standard deviation). The probability level for statistical significance was P < 0.05, and either parametric or non-parametric tests were used to compare different treatment groups.

Results and discussion

The temperature profile in the composting phase (first 28 days) of the different treatments is shown in figure 3.1. None of the treatments had a temperature rise above 33 ℃, which did not meet the requirements of EPA (Environmental Protection Agency) PFRP (Process to fungal reduction pathogens) contained in US-EPA 40 CFR Part503 (Hay, 1996). Although temperature development is an indicator of microbial activity (Jimenez and Garcia, 1991), the reduced temperatures observed may be a result of high moisture content (70%) of the material rather than microbial deficiencies. Thus, it is possible that higher temperatures can be reached if the initial moisture content of the material is lower upon loading. On the other hand, low temperatures may help preserve N in the composted material, as high temperatures may cause N to be NH at an early stage of composting₃High losses in the form (Sanch ez-Mondero et al 2001).

According to low temperature and EPA requirements one decides to perform analyses of total coliform, escherichia coli and salmonella in the final product. The presence of coliform bacteria is often used as an indicator of the overall hygienic quality of soil and water environments and is easy to detect (Hassen et al, 2001). Coli is the most representative bacterium of the faecal coliform group (Le Minor, 1984) and is therefore useful as an indicator of the presence of faecal coliforms. The presence of salmonella is considered a major problem of the hygienic quality of the compost, since it can cause diseases from contamination (Hay, 1996).

Coli or salmonella was not detected in any of the products, which means that the final product in this study should be safe for general distribution. The total number of coliforms is 2430 and 2903CFU g^-1In the meantime.

Percentage of CO in air₂And O₂The levels are shown in figures 3.2 and 3.3, with the maximum activity observed on the first 8 days. This corresponds to the temperature rise observed, which is normal in the usual composting process (Tuomela et al, 2000). Nutrient parameters (TOC, P) treated differently at loading_{[ Total]}、P-Bray 1、NH₄、NO₂And NO₃) Shown in table 3.1, and upon loading, no significant difference in the measured parameters was observed between the treatments with SS (P > 0.05). The average percent change in these parameters after composting and worm composting is shown in table 3.2. There was no significant difference in the mean percent change in TOC among the different groups (P > 0.05). This is because the temperature is not higher than 33 ℃ and C and CO are present in the treatment₂The fact that the form is least lost from the system.

All treatments with SS showed a significant increase in total P from 78.60- > 100%. Although all treatments showed an increase in P-Bray 1 values, the increase was statistically significant only in the SS + WC and SS + WC + EM groups (P < 0.05). Ghosh et al (1999) found that the organic waste from worm composting released relatively large amounts of P-Bray 1. They attribute this to the fact that earthworms acquire P as a nutrient for their synthesis in vivo and release the remaining P in a mineralized form, and presume that vermicompost may be an effective method for producing better P nutrition from organic waste. This is in contrast to other studies of soluble P reduction after composting (Vuorinen and saharanen, 1997) and after worm composting (Ndegwa and Thompson, 2001).

The concentration of N in the composted waste material is one of the most important factors in research to determine its agronomic value, and NH₄And NO₃Is of most interest because it is directly assimilable by the root system of the plant (Sanch é z-Mondero et al 2001). NH in all treatments containing SS₄Display 92.57->A significant (P < 0.05) decrease of 100%, whereas the WC treatment showed an increase over 100% with a practical final value of 1.77. + -. 0.80mmol L^-1。NO₂The levels of (c) showed a significant (P < 0.05) increase in all treatments with SS, while no significant (P > 0.05) change was observed in WC treatments. According to Sanch ez-Mondero et al (2001), compostedNO in the material₂Is a clear indication of anaerobic conditions during composting. This is due to the high moisture content of the material, which leads to the development of an anaerobic microenvironment. All treatment groups showed NO₃Significant (P < 0.05) increase over 100%. This can be explained by the fact that nitrogen-containing compounds evolve during composting as follows:

(Nitrosomonas)

(Nitrobacter)

However, there were differences in the following range of significance (P < 0.05) between the different treatments; SS + WC + e/w and SS + WC + EM + e/w > SS + WC and SS + WC + EM > WC.

At the end of the study, NO₃Is higher than NH₄This indicates that the correct composting process was performed (Finstein and Miller, 1985). Further, NH in all the treatments in the range of 0.011 to 0.0016 except in the WC treatment (0.27)₄∶NO₃All below 0.16 (Table 3.2), which is an indicator of compost maturity (Zucconi and de Bertoldi, 1987). There were no significant (P > 0.05) differences between the proportions in the SS-containing treatment, showing no differences in the evolution of nitrogen-containing products between compost, microbial inoculation and vermi compost.

The physical parameters (TS, VS, ash,% NDF,% lignin and% cellulose) and pH of the different treatments at the beginning of the experiment are shown in table 3.3, where no significant (P > 0.05) differences were observed in the parameters between the different groups. The average percent change in these parameters after the end of composting and worm composting is shown in table 3.4, where no significant (P > 0.05) difference was observed in WC treatment. The pH of WC showed a 5.75% decrease (P > 0.05) after 112 days of composting and worm composting, while those treated with sewage sludge showed an increase between 13.67 and 26.47%, and were both statistically significant (P < 0.05). This follows the alkaline trend of the pH during composting, where an initial decrease is observed due to the formation of organic acids, followed by an increase as a result of the release of ammonium (Tuomela et al, 2000). TS and ash content showed an overall increase, while VS and lignin showed an overall decrease, but these changes were statistically significant only in the treatment of vermicompost (P < 0.05).

According to Neuhauser et al (1988), an increase in the ash content and a decrease in VS are indicators of the stabilization of the compost material. The increase in TS is due to the fact that the worm composted material is physically degraded and therefore has an increased density, and the moisture content of the material (as a function of TS) is significantly lower. The material was also observed to show a volume reduction, although this was not quantitative. This volume reduction and moisture content reduction is associated with reduced handling and transportation costs.

The% NDF and% cellulose decreased significantly (P < 0.05) in all treatments with SS, and there was no significant (P > 0.05) difference between the different treatments. Cellulose degradation is associated with microbial biomass (Entry and Bachman, 1995) and can also be used by surface earthworms as a direct food source (Zhang et al, 2000), but reduces soil biomass after passing through the earthworm gut (Zhang et al, 2000), which may explain why cellulose decomposition is partially higher in earthworm-free treatments, although not statistically significant (P > 0.05). A significant (P < 0.05) reduction in% lignin was observed only in the treatment of two worm composts. This is due to lignin degradation regulated by the thickness of the material (Tuomela et al, 2000) and the fact that earthworms feed, grind and digest organic waste, converting it into finer material (Aranda et al, 1999).

Entry and Bachman (1995) also postulated that cellulose rather than lignin degradation is associated with microbial biomass, while Faure and Deschamps (1991) found that inoculation of organic waste with cellulolytic and lignin-lytic bacteria had no effect on degradation. Further, earthworms can consume materials with high lignin content, resulting in a persistent population size (Senpati et al, 1999).

The results of the particle size analysis are given in table 3.5 and expressed as geometric mean and geometric standard deviation and percent change. Worm composting with EM inoculation has the largest reduction in particle size, followed by no inoculation worm composting. These two groups also showed low heterogeneity, represented by a higher geometric standard deviation, observed. This is due to the presence of biologically inactive materials such as plastics (a by-product of an explosion used in mining) in the wood chips.

Thus, from the decrease in TS and VS and the increase in ash content, it is presumed that vermicomposting industrially produced wood chips and sewage sludge is better than composting it alone. It was also shown that only worm composting showed a significant reduction of lignin and that the addition of microbial inoculation did not increase the rate of decomposition.

Example 4

This embodiment refers to the following additional figures, wherein:

fig. 4 depicts a graph of mean body weight (g) ± SD of earthworms (e.fetida) (n 150) over 84 days. Significant difference (P < 0.05). (SS-sewage sludge; WC-wood chips; EM-microbial inoculation).

Materials and methods

Samples of air-dried Wood Chips (WC) and Sewage Sludge (SS) were again obtained from platinum ore.

The earthworm (e/w) species earthworm (e.fetida) ("tiger worm") was again used. A commercial microbial preparation (EM)_TM) For inoculation experiments, the preparation mainly comprises Pseudomonas, Lactobacillus and Saccharomyces species.

Substrates for applications

The application of a mixing ratio of 3: 1 (dry weight kg)^-1) WC and SS mixture of (a). The dry ingredients were mixed and humidified with distilled water to a moisture content of 70% (by weight). Each of 2 treatment groups with 3 replicates, consisting of WC + SS and WC + SS + EM mixtures, was studied. The substrate was placed in a plastic worm box (60X 40X 30cm), placed in an environmental chamber (25 ℃) and composted for 28 days. 100 mature worms were introduced after a 28-day composting period. This is done to avoid exposing the worms to the high temperatures possible in the initial thermophilic phase of composting.

Success rate of growth and reproduction

After a 28-day composting period, worm biomass was determined and the moisture content of the substrate was monitored every 14 days during period 94. Biomass was determined by taking 50 worms from each container, washing them in distilled water and drying them on paper towels. It was then weighed in a water-filled weighing boat using a Sartorius balance. This is done to prevent the worms from drying out and thereby affecting the weight of the earthworms.

Viability of egg bags was determined by randomly harvesting 72 egg bags from each container and placing them in multiple dishes filled with distilled water. The water in these dishes was replaced every 3 days to prevent bacterial growth which could negatively impact the results. The hatching egg bags and the number of hatchlings in each egg bag were recorded over 4 weeks.

Heavy metal analysis

Before and at the end of the experiment, 9 earthworms were taken from each group from the substrate. These worms were then placed on wet filter paper in petri dishes for 24 hours to allow for decontamination of their intestinal contents. This is done to prevent misleading of results regarding the actual heavy metal content in body tissue due to the presence of heavy metals in the intestinal content. After this 24 hour period, the worms were washed in distilled water, dried on paper towels and freeze killed. They were weighed individually and frozen (-74 ℃) in multi-top vials for heavy metal analysis in later stages. Substrate samples were also taken, placed in plastic bags and refrigerated until heavy metal analysis. Worms andcompost samples were digested as described by Katz and Jennis (1983). The samples were individually dried and milled and then ash at 550 ℃. They were then placed individually in test tubes and 10mL of 55% nitric acid (HNO) was added₃). It was left overnight at room temperature to initiate the digestion process. The samples were heated at 40-60 ℃ for 2 hours, then at 120-130 ℃ for 1 hour the following day, after which they were allowed to cool. 1mL of 70% perchloric acid (HClO) was added and the mixture was heated again at 120 ℃ and 130 ℃ for 1 hour. The sample was allowed to cool before adding 5mL of distilled water. The sample was then heated again at 120-. Allowing the sample to be finally cooled before microfiltration.

The solution was filtered through Whatman No. 6 filter paper to 20cm using a Sartorius microfilter-holder and plastic syringe³In a volumetric flask of (1). Adding distilled water to make up to 20cm³The filtrate of (1). Make the 20cm³The solution was filtered through 0.45 μm Sartorius nitrocellulose filter paper into a polyethylene container and the different metals were analyzed by inductively coupled plasma spectroscopy (ICP-AES).

Statistical analysis of data

SigmaStat was used as data in this study^®Computer software package analysis was performed and all values are expressed as mean ± SD (standard deviation). The probability level for statistical significance was P < 0.05, and either parametric or non-parametric tests were used for the comparative treatment groups.

Results

There was no stage during the study where any mortality was observed and the average biomass change of earthworms (e.fetida) is shown in fig. 4. The average biomass of earthworms in the SS + WC treatment was 0.44. + -. 0.01g and that in the SS + WC + EM treatment was 0.43. + -. 0.02g before introduction into the mixture treatment. There was no significant difference between these two values (P > 0.05). On day 14, the average biomass of earthworms reached a maximum of 0.81. + -. 0.02g and 0.77. + -. 0.02g in the SS + WC and SS + WC + EM groups, respectively, which were significantly higher than the initial biomass (P < 0.05). From day 14 to 84, the average biomass decreased to 0.49. + -. 0.03g in SS + WC and 0.51. + -. 0.01g in SS + WC + EM, with a significant difference between the two values (P < 0.05). These values are all significantly higher than the initial biomass (P < 0.05).

The average hatching success rate of the oocytes generated in the SS + WC group was 46.8 ± 2.4% (n ═ 216), and significantly (P < 0.05) was lower than 68.0 ± 2.8% in the SS + WC + EM group. The mean number of hatchings per egg bag was 2.7. + -. 0.1 for SS + WC and 3.0. + -. 0.2 for the SS + WC + EM group, with no significant difference between the two values (P > 0.05).

The heavy metal content of Al, As, Cu and Ni in the two substrate mixtures is summarized in table 4.1 and no significant difference was found for these selected metals (P > 0.05). The initial and final body heavy metal loads present in the earthworm tissue are shown in table 4.2. Initially, there was no statistical difference between the heavy metal content of the earthworm body tissue in the two groups (P > 0.05). At the end of the experiment, the heavy metal content of earthworms in SS + WC was significantly (P < 0.05) higher than that of all heavy metals measured at the beginning, but only lower than 0.05. mu. g.g^-1Except for As at the detection limit of (1). Heavy metals showed no significant difference (P > 0.05) after 84 days in earthworms exposed to SS + WC + EM. The bio-concentration factor (BCF) for different heavy metals in the earthworm body tissue after the 84-day worm composting period is shown in table 4.3. It is evident that the BCF of earthworms in the SS + WC group for Al, Cu and Ni is almost twice that in the SS + WC + EM group.

Discussion of the related Art

From the results (fig. 4 and tables 4.1-4.3), it is evident that earthworms in both treatment groups were exposed to a mixture of contaminants including Al, Cu and Ni. This makes the estimation of toxicant action difficult, since the actual risk to the organism is 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-Fordsmann et Al, 1998) on growth and reproduction are well documented, but there is currently no or very little information available for Al. In addition, literature on the effect of these metals as a mixture on earthworms (e.fetida) is lacking. With respect to the risks that these metals may pose in the rehabilitation program applications, Al, Cu and Ni are all higher than the range proposed for agricultural use by DWAF (1996). These factors should be considered in selecting the plant species for rehabilitation and monitoring the amount of infiltration of these metals into the groundwater.

Growth data are comparable to previous studies in which earthworms (e.fetida) were found to reach an average biomass of ± 0.45g under optimal conditions (Reinecke et al, 1992). The fact that the average biomass of worms exposed to SS + WC was significantly (P < 0.05) lower than those exposed to SS + WC + EM was a direct cause of the bioavailability of heavy metals in these substrates. However, both groups showed a decrease in biomass after 14 days (fig. 4), which may be attributed to the presence of elevated heavy metal concentrations. Growth can therefore be considered as a parameter to estimate the susceptibility of Al, Cu and Ni to the action of earthworms (e.fetida). This is in contrast to the previous pair of CuNO₃Studies of the effect of Cu in its form on growth have found agreement (Reinecke and Reinecke et al, 1996), they found that earthworms (e.fetida) grow at 200 μ g.g^-1The substrate concentration of (a) is negatively affected.

Growth is considered an endpoint and it is therefore assumed that vermicomposting of wood chips and sewage sludge using earthworms (e.fetida) is economically feasible. In view of the fact that earthworms perform better in mixtures containing microbial inoculations and end-point with average biomass, it is expected that better results will be produced in large scale worm composting techniques.

The mean hatching success rate, which can be considered as the end point of the reproductive success rate, was significantly (P < 0.05) higher in the SS + WC + EM group than in the SS + WC group, although there was no difference in the mean hatching number between the two (P > 0.05).

Venter and Reinecke (1988) concluded that the average hatching success rate of the bags produced by earthworms (e.fetida) was 73%, and that each bag produced an average of 2.7 hatchlings. The hatching success rate produced by worms in the SS + WC + EM mixture was 68% better than 73% as determined by Venter and Reinecke (1988), but the hatching success rate of the egg sacs in the SS + WC mixture was very low, 45%. With respect to having high Ni (551. mu. g.g)^-1) And Cu (315. mu. g.g)^-1) Data on incubation success in SS + WC substrate at concentrations are consistent with previous authors' results. LockAnd Janssen (2002) report EC for Ni₅₀Based on the egg pocket production, 362 μ g.g^-1Spurgeon and Hopkin (1995)) Worm propagation was found to be significantly reduced in copper contaminated soils. Reinecke and Reinecke (1996) found exposure to 200.mu. g.g^-1Earthworms (e.fetida) in copper concentration do not produce egg sacks. Therefore when estimating the potential for using earthworms (e.fetida) in worm compost wood chips and sewage sludge, hatching success is a more sensitive parameter than growth.

The fact that the hatching success rate was higher in the groups inoculated with the microorganisms may be due to the fact that Ni and Cu are less available to the worms, which Ni and Cu have a detrimental effect on the reproductive success. Microorganisms are able to concentrate metals both actively (bioaccumulation) and passively (bioadsorption) (Unz and Shuttleworth, 1996). It has been shown experimentally that Saccharomyces (Simmons et al, 1995) and Pseudomonas (Churchill et al, 1995) show large changes in the bioabsorption of metals, both of which are present in the inoculum. This may provide a possible explanation for the disparity between growth and reproductive success rates observed between the two groups. This fact can be confirmed by the heavy metal body load observed in the earthworm body tissues, where the inoculum-containing worms in the substrate had significantly low (P < 0.05) levels of Al, Cu and Ni, which is also reflected by the calculated BCF.

Conclusion

It is assumed that the growth of earthworms (e.fetida) is not inhibited when used as vermicompost species or microbial inoculated additives for industrially produced wood chips and sewage sludge. The success rate of reproduction of earthworms in the SS + WC-treated group was decreased, and Al, Cu and Ni were biologically accumulated in their body tissues. In contrast, earthworms in the treatment group with the microbial inoculum added did not bioaccumulate any heavy metals in their body tissues and had a significantly higher reproductive success rate than their equivalent in the treatment without the microbial inoculum. This shows that the microorganisms present in the inoculum make the heavy metals present in the wood chips and sewage sludge mixture unusable by their bioadsorption or bioaccumulation.

It therefore appears that the most economically viable route to bioconversion of wood chips and sewage sludge with earthworms (e.fetida) is the addition of microbial inocula.

Example 5

This embodiment refers to the following additional figures, wherein:

fig. 5 is a perspective view of a hay trail (windrow) composting or worm composting media for treating mining motile bodies in accordance with the present invention.

From experimental studies it can be concluded that for successful composting of Wood Chips (WC) and Sewage Sludge (SS) a 3: 1 mixing ratio is required and that the composting/vermicomposting process extends to 4-6 months.

For commercialization of the method according to the invention, the first step is to compost WC and SS for 30 days by constructing a hay column, an example of which is shown in fig. 5. Thereafter the material was covered with a net (to prevent bird predation) and vermicompost was carried out for 4-5 months with earthworms (Eiseniafetida) at a rate of 25g worms per kg material.

As shown in FIG. 5, the optimum size for constructing a hay row is 2 tons of compost mixture per meter of length, 1m high and 2m wide. This means that 50kg earthworms are applied per hay row.

The compost thus obtained and the medium of worm compost are then mixed into the tailings as described in examples 1 and 2 above.

It has been found that the compost and vermicompost media according to the invention provide advantageous alternatives and/or additions to soil improvement using topsoil, and that the subsequent waste wood chips and sewage sludge, which are the main sources of organic carbon and nitrogen, are the sources of essential nutrients and organic matter for the growing organisms when subjected to bioconversion according to the invention. Wood chips are further advantageous organic modifiers in the process of vegetation restoration and the main reason for their use as modifying means is their ability to promote cation exchange capacity, thereby reducing alkali saturation and improving the ability of mucus to adsorb excess salts. Wood chips can also improve the physical properties of the growth medium by increasing water retention. Organic materials can also stimulate biological activity, which is essential for nutrient recycling.

A further advantage of the present process is that the waste produced by mining, such as slime, wood chips and sewage, is used to recover tailings and to reduce soil, groundwater and air pollution.

It will be appreciated that detailed variations to the media and method of treating tailings of a mining activity in accordance with the present invention are possible without departing from the scope of the appended claims.

Claims (31)

1. A method of treating a tailings body of a mining activity, the method comprising the step of applying wood particles to the tailings body.

2. The method of claim 1, wherein the wood particles are wood chips recovered from waste wood as a byproduct of a mining activity.

3. A method according to claim 2, wherein the wood chips are in the form of wood ore pillars which disintegrate in an explosive operation.

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

5. The method according to claim 4, wherein the acid is nitric acid (HNO)₃)。

6. A method according to any one of the preceding claims, wherein the wood particles are applied to the surface layer of the gangue bodies.

7. A method according to claim 6, wherein the particles are applied in the form of a coating.

8. A process according to any one of claims 1 to 5 wherein the particles are processed into a residue.

9. A method according to claim 8, wherein the particles are excavated into a tailings body.

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

11. A method according to any one of the preceding claims, wherein the particles are applied to residual ore present in the form of a dam to restore the dam.

12. A method according to any one of claims 1 to 10, wherein the particles are applied to the residuum during its formation.

13. A process according to any one of the preceding claims, wherein the wood particles are applied at a rate of 60 to 90 tonnes per hectare of tailings dam surface.

14. A method according to any one of the preceding claims, including the step of composting the wood particles prior to the step of applying the particles to the gangue bodies.

15. The method of claim 14, wherein the step of composting the wood particles comprises the step of vermicomposting the particles.

16. The method of claim 15, wherein the step of composting the wood particles further comprises the step of mixing the particles with another source of organic material.

17. The method of claim 16, wherein the source of the other organic material comprises sewage.

18. The method of claim 17, wherein the wood particles and the wastewater are mixed to form a compost, which may thereafter be inoculated with worms to form a worm compost medium.

19. A method according to claim 18, wherein the worms may be from the species earthworm (Eiseniafetida).

20. A method according to claim 18 or claim 19, wherein the wood particles are mixed with the effluent 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 growing selected plants on the treated ore residues.

22. The method according to claim 21, wherein the plant is selected from the group consisting of Tribulus ciliate variety Molopo; tribulus terrestris var Gayndah; eragrostis lehmanniana (Lehmann's Love Grass) and Saxatilis flexneri and mixtures thereof.

23. A method of treating a residual ore body in a mining activity substantially as herein described and illustrated.

24. A tailings ore body treated according to the process of any of claims 1 to 23.

25. A composted medium for treating mining motile ore bodies, the medium comprising a mixture of wood particles and another source of organic material.

26. The medium of claim 25, wherein the wood particles are wood chips recovered from waste wood as a byproduct of a mining activity.

27. A medium according to claim 25 or 26, wherein the wood particles are in the form of wood ore pillars which disintegrate in an explosive operation.

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

29. The method according to any one of the preceding claims, wherein the mixture is further worm compostable.

30. A medium according to any of claims 25-29, further comprising a selection of microorganisms.

31. A medium for treating residual ore bodies in mining activities substantially as herein described and illustrated.

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