Dimitra Zaharaki

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.

Efficiency of pecan shells and sawdust biochar on Pb and Cu adsorption

AbstractIn the present study, two different by-products, pecan shells, and sawdust obtained from the region of Chania, Crete, Greece, were subjected to slow pyrolysis over a temperature range of 250–550°C, for the production of biochar. The quality of the produced biochars was assessed by evaluating their main properties, namely pyrolysis yield, pH, volatile matter and char content, surface area, and C, H, S, N content. Thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy were used for the identification of the morphology and structure of the produced biochars. The potential of selected pecan shells and sawdust biochars to adsorb Pb and Cu from synthetic solutions was also assessed.

Assessment of biochar as feedstock in a direct carbon solid oxide fuel cell

The feasibility of employing biochar as a fuel in a direct carbon fuel cell (DCFC) or a hybrid carbon fuel cell (HCFC) is investigated in the present study, by utilizing bare biochar or biochar/carbonate mixture as feedstock, respectively. Three different types of biochars, i.e., pistachio shells (PI), pecan shells (PE) and sawdust (SD) are used as feedstock in a solid oxide fuel cell (SOFC) of a type: Biochar|Co–CeO2/YSZ/Ag|Air. All samples were characterized by means of chemical composition (ultimate/proximate analysis), mercury porosimetry, N2 adsorption–desorption isotherms (BET method), thermogravimetric analysis (TGA), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM), to obtain a close correlation between cell performance and biochar characteristics. The electrochemical measurements reveal that the optimum performance, in terms of maximum power density (Pmax), is obtained for the PI biochar, which demonstrated a power output of 15.5 mW cm−2 at 800 °C, compared to 14 and 10 mW cm−2 for PE and SD biochars, respectively. The obtained cell performance results are interpreted on the basis of biochar physicochemical characteristics and AC impedance spectroscopy studies. The superior performance of PI biochar is attributed to a synergistic effect of several physicochemical characteristics, involving the porosity, the acidity, the volatile matter, the carbon and hydrogen content as well as the population of oxygenated surface functionalities.

Microstructural characteristics and adsorption potential of a zeolitic tuff–metakaolin geopolymer

The aim of this work is to investigate the microstructural characteristics and the adsorption potential of zeolitic tuff–metakaolin (ZM) geopolymers. For the identification of microstructure, X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses were used. XRD showed that mordenite, a major zeolite mineral, disappeared upon geopolymerization, while SEM showed that ZM-geopolymers exhibit a uniform porous matrix consisting of nanoparticles (~40 nm). The adsorption efficiency of ZM-geopolymers was assessed using solutions containing 250 mg/L copper. The experimental results show that the maximum adsorption efficiency (7.8 mg Cu 2+ /g of adsorbent) is observed at an initial zeolitic tuff/metakaolin ratio of 0.5 which indicates that ZM-geopolymers can be used in environmental applications including the clean-up of industrial effluents and wastewaters.

Morphology of Modified Biochar and Its Potential for Phenol Removal from Aqueous Solutions

In the present study, the efficiency of phenol removal from synthetic aqueous solutions by chemically modified biochar with the use of 1M KOH or 1M FeCl3 was investigated. Initially, biochar was produced after slow pyrolysis of three different agricultural wastes, namely pistachio (Pistacia vera L.) shells, pecan (Carya illinoinensis) shells and wood sawdust. The quality of biochar was assessed by evaluating its main properties, such as pH, surface area, porosity and C content. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) were used for the identification of biochar’s structure. The efficiency of phenol removal from synthetic solutions was assessed with the use of kinetic and equilibrium experiments. The experimental results show that the KOH-modified biochar exhibited the highest phenol removal efficiency. Hydrophobic sorption on its surface is the main phenol removal mechanism. The pseudo-second order model fits best the kinetic data, while the Freundlich model, as deduced from an equilibrium study describes very well sorption of phenols on all biochars examined.

Origin of Recalcitrant Heavy Metals Present in Olive Mill Wastewater Evaporation Ponds and Nearby Agricultural Soils

The present study attempts to elucidate the origin of recalcitrant heavy metals, namely Cr, Ni, and Mo, present in olive mill wastewater (OMW) evaporation ponds and nearby agricultural soils. Steel corrosion tests were carried out using several types of alloys (316L, 316, 304, and St 37-2) while sludge and soil samples were collected from the walls of active and inactive OMW evaporation ponds as well as from nearby soils and analyzed in order to elucidate the presence of heavy metals of interest. Experimental results prove that corrosion of high quality steels is extremely limited and is mainly caused in solutions characterized by high chloride concentration. It is therefore assumed that the presence of recalcitrant heavy metals in soils is the result of past (between 1970 and 2000) olive oil milling activities when inferior quality steel equipment was used.

Assessment of Human and Ecosystem Risk Due to Agricultural Waste Compost Application on Soils: A Review

Agricultural wastes (AW) are often characterized by varying pH and substantial contamination potential, which are mainly related to their high organic load, thus affecting—when improperly disposed of—soils, living organisms, and water bodies. Composting of AW is the most commonly used management option and results in the production of soil improver that enhances crop growth and contributes to agricultural sustainability. This study aims to present the framework for assessing human and ecosystem risk when compost produced from AW is applied on soil. In order to develop this framework, issues such as origin, composition and pre-treatment of AW, application rates on soils, bioavailability and mobility of contaminants present in compost, exposure routes and rates as well as determination of the fate of contaminants in soil, air, and water, should be taken into consideration.

Removal of heavy metals from leachates using organic/inorganic permeable reactive barriers

ABSTRACT In the present experimental study, the efficiency of permeable reactive barriers (PRBs) containing organic material mixed with zero-valent iron, fly ash or red mud to remove heavy metals from leachates was assessed. Upflow laboratory column experiments were carried out to assess system efficiency in terms of Cu, Zn, Ni and Mn removal. The initial concentration of each metal ion in the feed was 50 mg/L. X-ray diffraction as well as scanning electron microscopy and energy dispersive spectrometry were used to identify new mineral phases and to identify metal removal mechanisms. Results and analyses show that sorption and precipitation of metals as sulphides, hydroxides and other hydrated phases are the dominant metal removal mechanisms.

Assessment of reactivity of sulphidic tailings and river sludges

ABSTRACT The aims of this work were: to assess the long-term reactivity of sulphidic wastes disposed of in a tailings dam at Bor, Serbia; to assess the reactivity of the sludges formed in a stream receiving acidic effluents; and to estimate the risk for the wider ecosystem. The laboratory assessment was carried out according to a slightly modified AMIRA protocol, using conventional free-draining leach columns. Deionized water and simulated acid rain were used as leaching media. The experimental results over a period of c. 70 weeks show increased solubilization for a number of metals and subsequently high risk for contamination of surface- and groundwater. Finally, feasible and effective remediation measures are proposed.

Assessment of Aquifer Vulnerability in an Agricultural Area in Spain Using the DRASTIC Model

The assessment of aquifer vulnerability is a very important task, especially in agricultural areas because the quality and availability of groundwater affects both the sustainability of agriculture and the quality of life. In this study, an integrated approach is considered, with the use of the generic and agricultural DRASTIC models as well as a geographic information system (GIS), to assess groundwater vulnerability in the agricultural area of Barrax, in the province of Albacete, in Spain. Seven parameters—depth to water, net recharge, aquifer media, soil media, topography, impact of vadose zone media, and hydraulic conductivity of the aquifer (DRASTIC)—have been considered as weighted layers to enable an accurate groundwater risk mapping. The results of the generic DRASTIC model indicated very low vulnerability to contamination for Barrax groundwater due to limited urban and industrial development in the wider area. However, agricultural activities impose pressure to groundwater resources and the results of the agricultural DRASTIC model show that 6.86% of the study area is characterized by very high, 2.29% by high, 47.28% by medium, 38.28% by low, and the remaining 5.29% by no vulnerability to groundwater contamination. The distribution of nitrate concentration in groundwater in the area under study is quite well correlated with the agricultural DRASTIC vulnerability index. Sensitivity analysis was also performed to acknowledge statistical uncertainty in the estimation of each parameter used, to assess its impact, and thus to identify the most critical parameters that require further investigation. Depth to water and impact of vadose zone are the parameters that had the most noticeable impact on the generic DRASTIC vulnerability index followed by the soil media and topography. In contrast, the agricultural DRASTIC method is more sensitive to the removal of the depth to water parameter followed by the topography and the soil media parameters.