Kostas Komnitsas

Use of organic covers for acid mine drainage control

Abstract Organic covers may be used to prevent diffusion of oxygen into reactive sulphide wastes and subsequently to eliminate sulphide compounds oxidation and generation of acidic waters. The main advantages over other types of covers are related with their low hydraulic permeability, high cation exchange capacity and high alkalinity. In addition, the establishment of organic covers, which is considered as a low cost solution for the prevention of acid mine drainage generation, does not disturb the natural environment, since they consist of industrial wastes rather than natural materials and allow the development of vegetation, which improves the aesthetics of the reclaimed areas. However, treatment of municipal sewage sludge is necessary prior to discharge, in order to minimize potential health and environmental risks, resulting from the presence of toxic elements. In the present paper, all processes associated with the function of an organic cover are described and discussed, including potential health and environmental risks resulting from land application of municipal sewage sludge. In addition, preliminary laboratory data, derived from the application of organic covers over reactive sulphidic concentrates are presented and discussed, in order to evaluate the performance of the covers and to determine the critical factors affecting their performance. The final aim of this research work is the development of an experimental model, that predicts the performance of an organic cover, by taking into account critical parameters such as annual rainfall rate, organic material height, initial moisture and moisture under saturation conditions.

Effect of synthesis parameters on the compressive strength of low-calcium ferronickel slag inorganic polymers

The wide range of physical and chemical properties of inorganic polymers, also known as geopolymers, commonly formed by alkali activation of aluminosilicates, makes these materials useful for a variety of applications. In the present experimental study inorganic polymers are synthesised from low-Ca electric arc ferronickel slag. The effect of experimental conditions on the compressive strength of the final products is assessed. A number of techniques, namely XRD, FTIR and TG-DTG were used to identify new phases and subsequently elucidate to some degree the mechanisms involved. Finally, the paper discusses briefly the potential of inorganic polymer technology as a feasible option for the utilisation of certain potentially hazardous mining and metallurgical wastes towards an increased sustainability of the wider minerals sector.

Disposal of olive oil mill wastes in evaporation ponds: Effects on soil properties

The most common practice followed in the Med countries for the management of olive oil mill wastes (OMW) involves disposal in evaporation ponds or direct disposal on soil. So far there is lack of reliable information regarding the long-term effects of OMW application on soils. This study assesses the effects of OMW disposal in evaporation ponds on underlying soil properties in the wider disposal site as well as the impacts of untreated OMW application on agricultural soils. In case of active disposal sites, the carbonate content in most soils was decreased, whereas soil EC, as well as Cl(-), SO(4)(2-), PO(4)(3-), NH(4)(+) and particularly K(+) concentrations were substantially increased. Soil pH was only marginally affected. Phenol, total N, available P and PO(4)(3-) concentrations were considerably higher in the upper soil layers in areas adjacent to the ponds. Available B as well as DTPA extractable Cu, Mn, Zn and Fe increased substantially. Most surface soil parameters exhibited increased values at the inactive site 6 years after mill closure and cease of OMW disposal activities but differences were diminished in deeper layers. It is therefore concluded that long-term uncontrolled disposal of raw OMW on soils may affect soil properties and subsequently enhance the risk for groundwater contamination.

Artificial Inoculation—Perspectives in Tailings Phytostabilization

ABSTRACT Intensive mining and processing activities worldwide resulted in the generation of huge amounts of waste (tailings), generally characterized as toxic, radioactive, and/or hazardous. The exposure potential and, hence, the risk posed by such wastes is enhanced by a general lack of vegetation. Phytostabilization has proven to be efficient in reducing this risk. However, establishing vegetation on tailing dumps may be expensive due to the intensive use of amendments and chemical fertilizers. In this article, investigations on artificial inoculation of mine tailings with bacterial strains as a means to improve the development of vegetative covers and reduce application cost by eliminating chemical fertilization are presented and discussed. The development of plants and microbial communities from tailings, as well as the impact of inoculation on metal uptake in plants, were studied. Experiments were carried out in greenhouse using two types of mine tailings (phosphogypsum and sulphidic tailings) from the Romanian Black Sea coast. Indigenous herbaceous plants were cultivated on tailings with the addition of chemical fertilizers versus bacterial inoculation. After a 6-month experimental period, excellent plant growth, which is associated with a rich microbial community, was observed in all inoculated treatments, in contrast with poor plant growth and microbiota from the chemical fertilization treatments alone. Additionally, artificial inoculation improved plant resistance to heavy metals by reducing the uptake of some toxic metals. Once a rich microbial community is established, inoculation may be discontinued. Based on these results, efficient and cost-effective phytostabilization schemes can be proposed.

Solid phase studies and geochemical modelling of low-cost permeable reactive barriers

A continuous column experiment was carried out under dynamic flow conditions in order to study the efficiency of low-cost permeable reactive barriers (PRBs) to remove several inorganic contaminants from acidic solutions. A 50:50 w/w waste iron/sand mixture was used as candidate reactive media in order to activate precipitation and promote sorption and reduction-oxidation mechanisms. Solid phase studies of the exhausted reactive products after column shutdown, using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), confirmed that the principal Fe corrosion products identified in the reactive zone are amorphous iron (hydr)oxides (maghemite/magnetite and goethite), intermediate products (sulfate green rust), and amorphous metal sulfides such as amFeS and/or mackinawite. Geochemical modelling of the metal removal processes, including interactions between reactive media, heavy metal ions and sulfates, and interpretation of the ionic profiles was also carried out by using the speciation/mass transfer computer code PHREEQC-2 and the WATEQ4F database. Mineralogical characterization studies as well as geochemical modelling calculations also indicate that the effect of sulfate and silica sand on the efficiency of the reactive zone should be considered carefully during design and operation of low-cost field PRBs.

Environmental characterisation of the sulphidic tailings in Lavrion

Abstract Intensive mining and metallurgical activities in Lavrion over a time span of over 2700 years resulted in the formation of huge spoils of mining, milling and metallurgical wastes and tailings, most of them characterised as toxic and hazardous. Toxic elements are released by a number of mechanisms and migrate to the surrounding area, contributing to the widespread soil contamination. Three main types of spoils exist: sulphidic flotation tailings, oxidic-carbonaceous-silicate beneficiation tailings and metallurgical slags. This paper deals with the sulphidic flotation tailings. For the estimation of the risk that these tailings pose to the environment and for the conceptual development of a remediation strategy, complete characterisation was done according to the following methodology: Drillholes were placed within the spoils and undisturbed core samples were taken and characterised chemically and mineralogically, their net neutralisation potential (NNP) was determined using static tests and their toxicity using the EPA TCLP test, speciation of the toxic metals was determined in some cases using the sequential extraction technique and the bioavailable fraction determined by EDTA extraction. Some geotechnical characteristics of the spoils, as density and permeability were determined in-situ. Piezometers were installed within the boreholes and the pore water quality and level was monitored. The above information is being critically assessed and employed for the selection and design of the optimum rehabilitation scheme.

Treatment of waters polluted with radioactive elements and heavy metals by means of a laboratory passive system

Waters polluted with toxic heavy metals, radioactive elements, arsenic and sulphates were efficiently treated by means of a laboratory-scale passive system consisting of an anaerobic cell and a constructed wetland. These waters were polluted in a stream receiving leachates from an operating copper tailings dam and other effluents from man-induced activities at the area of Vromos Bay in Bulgaria. The anaerobic cell contained a mixture of horse, cow and sheep manure, spent mushroom compost, wheat straw and sawdust which were used as sources of carbon and energy by different metabolically interdependent microorganisms inhabiting the cell. The microbial dissimilatory sulphate reduction and the sorption on the organic matter were the main processes connected with the removal of pollutants. The effluents from the anaerobic cell were enriched in soluble organic compounds which were degraded in the constructed wetland containing rich microbial and plant cenoses. The effluents from the constructed wetland were suitable for use in the agriculture and industry.

Risk assessment and proposed remedial actions in coastal tailings disposal sites in Romania

Abstract Intensive mining and ore processing activities over the last fifty years concerning phosphate and polymetallic sulphidic ores at Navodari and Baia, by the Romanian Black Sea coast, have resulted in the production of millions of tonnes of hazardous wastes which contain high residual concentrations of heavy elements and radionuclides in mobile forms. At Navodari, where a chemical plant for the production of sulphuric acid and superphosphates operates, over 3,000,000 m 3 of phosphogypsum and 1,000,000 m 3 of pyritic cinders have been disposed of in several stacks and dumps. At Baia, over 1,200,000 † of copper tailings from the nearby located flotation plant have been disposed of since 1965 in three decantation ponds. Under the action of several physicochemical mechanisms, toxic elements contained in the tailings are mobilised migrate to the surroundings and cause severe and widespread contamination of soils, surface and ground waters and the Black Sea. In this paper, all the above mentioned sources of pollution that are currently directly or indirectly affecting humans, soils, freshwater ecosystems and the Black Sea, are identified and characterised Furthermore, in order to assess the level of risk posed by each source of pollution, at each affected area, a complete environmental characterisation study was undertaken followed by a risk analysis carried out on a source-pathway-target basis. Based on experimental and risk analysis data, a rehabilitation scheme is proposed for all affected areas, aiming at deactivating the pollution sources and rehabilitating the contaminated areas with remedial actions. This scheme involves mainly. removal of toxic and heavy elements from sulphidic tailings and leachates with biosorption and biosolubilisation techniques and development of a vegetative cover on phosphogypsum, cinders and sulphidic tailings.

Carbonate-rich mining tailings in Lavrion: risk assessment and proposed rehabilitation schemes☆

Abstract In Lavrion, Greece, the mining and metallurgical activities that were particularly intensive during the last century resulted in the generation of huge amounts of wastes, including acid-generating sulfidic tailings, carbonaceous tailings and slags. Their improper management in the past resulted in the migration of heavy metals to the surroundings, contributing to widespread soil contamination. As a result, the local population is exposed to multiple hazardous pollution sources. The present study aims to combine the available geochemical characterisation techniques and risk assessment tools in order to identify the specific risks associated with the carbonate wastes and determine the remedial measures required accordingly. The risk assessment study of the carbonate tailings resulted in the identification of three high-risk exposure routes for humans: direct contact, ingestion and inhalation of contaminated material. Plant uptake and secondary contamination of soils are rated as high-risk exposure routes only for ‘Savoura’ tailings. Quantification of the human health risks indicated that direct ingestion of contaminated particles is the most important exposure route for the intake of contaminants by humans. The intake of Pb, As and Cd by adults and children living in the vicinity of carbonaceous tailings was found to exceed the maximum tolerable risk. Based on the risk assessment results, several remediation options were examined, aimed at either removing the source or breaking the significant source–pathway–target relationships.

Bioremediation of a soil contaminated with radioactive elements

Abstract Some agricultural lands located in the Vromos Bay area, near the Black Sea coast, Southeastern Bulgaria, have been contaminated with radioactive elements (uranium, radium and thorium) and toxic heavy metals (copper, cadmium and lead) as a result of mining and mineral processing of polymetallic ores. Laboratory experiments carried out with soil samples from these lands revealed that an efficient remediation of the soils was achieved by an in situ treatment method based on the activity of the indigenous soil microflora. The treatment was connected with the dissolution of the contaminants in the upper soil horizons and their transfer into the deeply located soil horizons (mainly to the horizon B2) where they were immobilized as different insoluble compounds. The dissolution of contaminants was connected with the activity of both heterotrophic and chemolithotrophic aerobic microorganisms and the immobilization was due mainly to the anaerobic sulphate-reducing bacteria. The activity of these microorganisms was enhanced by suitable changes in the levels of some essential environmental factors such as water, oxygen and nutrient contents in the soil. On the basis of the above-mentioned laboratory results, the method was then applied under real field conditions in a heavily contaminated experimental plot of land located in the Vromos Bay area. Within 8 months of treatment, the contents of radioactive elements and toxic heavy metals in the soil were decreased below the relevant permissible levels.