Luigi Piga

Arsenic leaching by Na2S to decontaminate tailings coming from colemanite processing

AbstractColemaniteisacalciumboratemineralfromwhichboricacidandthenboratesareobtained.Theseproductsareusefulfordifferentapplications.Colemaniteleachingbysulphuricacidleadstoproductionofboricacid.Arsenicminerals,mainlyrealgarandorpiment,whichareoftenassociatedtogetherwithcolemanite,dependingonmineralparagenesis,arenotleachedbytheacid.Arseniccomponentscontaminatethetailingsresultingfromthechemicalprocess,mainlyconstitutedbygypsum.Sometimesthehigharsenicpollutionallowscharacterisingthetailastoxic,implyingveryhighdisposalcosts.Inordertoavoidthisdrawback,Ascontentingypsumwasreducedfromalevelupto2000ppmtoavaluelessthan500ppmafterNa 2 Sleaching.Reagentscon-sumption,pHandpulpdensitywereadjustedinordertoobtainamaterialthatdoesnotneedtobedisposedofinanexpensivelandfillasitissuitableforuseasacementadditiveandplaster. 2003ElsevierScienceLtd.Allrightsreserved. Keywords: Hydrometallurgy;Environmental 1.IntroductionBorates are very important chemicals applied inmetallurgy,inagriculture,inthenuclearindustryand,furthermore,inmanufacturingofglasses,glass-fibres,enamels and glazes, flame retardant and bleachingagents.Newapplicationsarecontinuouslyproposed:themostrecentonesinvolvetheuseofmetalborides,assuperconductors and thermoionic emitters, labelledboranes,inbiomedicalapplicationssuchasBNCT,andboroncagecompoundsforcaesiumseparationfromnuclearwaste(King,1999).Boratedepositsaremainlyconcentratedinafewareas:theworldslargestreservesofboratesoccurinAnatolia,inthesurroundingsoftheRedSea–Aegeanrift.Themostimportantdepositsofcolemanite(2CaO3B

Thermal treatment for recovery of manganese and zinc from zinc-carbon and alkaline spent batteries

The aim of this paper is the recovery of manganese and zinc from a mixture of zinc-carbon and alkaline spent batteries, containing 40.9% of Mn and 30.1% of Zn, after preliminary physical treatment followed by removal of mercury. Separation of the metals has been carried out on the basis of their different boiling points, being 357°C and 906°C the boiling point of mercury and zinc and 1564°C the melting point of Mn(2)O(3). Characterization by chemical analysis, TGA/DTA and X-ray powder diffraction of the mixture has been carried out after comminution sieving and shaking table treatment to remove the anodic collectors and most of chlorides contained in the mixture. The mixture has been roasted at various temperatures and resident times in a flow of air to set the best conditions to remove mercury that were 400°C and 10 min. After that, the flow of air has been turned into a nitrogen one (inert atmosphere) and the temperatures raised, thus permitting the zinc oxide to be reduced to metallic zinc by the carbon present in the original mixture and recovered after volatilization as a high grade concentrate, while manganese was left in the residue. The recovery and the grade of the two metals, at 1000°C and 30 min residence time, were 84% and 100% for zinc and 85% and 63% for manganese, respectively. The recovery of zinc increased to 99% with a grade of 97% at 1200°C and 30 min residence time, while the recovery and grade of manganese were 86% and 87%, respectively, at that temperature. Moreover, the chlorinated compounds that could form by the combustion of the plastics contained in the spent batteries, are destroyed at the temperature required by the process.

Fluoride Removal from Water by Adsorption on a High Alumina Content Bauxite

Drinking water contamination by fluoride is recognized as a major public health problem in many parts of the world. In fact, although fluoride is an essential trace element for animals and humans, excessive fluoride intake may cause adverse health effects. In this study we investigated the potential of a natural, high alumina content, bauxite for the removal of fluoride from contaminated water. Both batch and continuous experiments were performed. In continuous-flow column experiments, the effects of inlet fluoride concentration (5–50 mg L

Evaluation of the leachability of heavy metals from cement-based materials

A new leaching test on comminuted (0.125-2.0mm gradation) cementitious matrices, designated as Modified-Pore Water (M-PW) test, was developed to evaluate the effect of varying leachate pH (4-12.8) and/or liquid-to-solid, L/S, ratio (0.6-50 dm(3)/kg) on the availability factor, F(AV), of heavy metals. The M-PW test was applied to leaching of lead and zinc ions from ground Portland cement mortar incorporating Municipal Solid Waste Incinerator (MSWI) fly ash. Correlation of M-PW test results (F(AV)-L/S data) allowed the determination of the pore-liquid availability factor, F(AVP), at different leachate pHs. These F(AVP) values were utilized, in conjunction with a kinetic pseudo-diffusional model, to evaluate the leaching behavior of monolithic mortar specimens subjected to dynamic leaching tests (constant leachant pH 4 or 6).A good agreement was found between the effective diffusion coefficients, D(e), of lead and zinc ions calculated by such a methodological approach and those obtained from recognized microstructural models. In contrast, no satisfactory agreement was found when these D(e) values were compared with the ones calculated from the results of other availability tests on granular solid samples (NEN 7341 and AAT tests).

Use of cell wall degrading enzymes for the production of high-quality functional products from tomato processing waste

The feasibility of using tomato pomace, the solid waste resulting from the industrial processing of tomatoes, to produce a tomato oleoresin and a lycopene-enriched seed oil was investigated. The oil was obtained by cold-pressing the seeds, while the oleoresin was produced by pretreating the peel fraction of the waste with cell wall degrading enzymes. The latter consisted of polygalacturonase, pectin methylesterase, cellulase and hemicellulase. The enzymatic treatment followed by hexane extraction and solvent evaporation allowed the production of an oleoresin with a lycopene content of about 7% by weight. The oleoresin was incorporated in different proportions into tomato seed oil so as to obtain a functional oil with a lycopene content ranging from 30 to 600 ppm. The lycopene-enriched oil was characterized by official analytical methods and its potential use in the nutraceutical and cosmetic sectors was discussed.

Spent Tea Leaves as a Potential Low-cost Adsorbent for the Removal of Azo Dyes from Wastewater

Spent tea leaves (STL), a solid waste that is available in large amounts worldwide, was investigated as a potential low-cost adsorbent for the removal of two azo dyes, Reactive Green 19 (RG19) and Reactive Violet 5 (RV5), from contaminated waters. Preliminary experiments conducted on untreated STL showed that this material exhibited very low removal efficiencies (<10 %). By contrast, thermal activation of STL (200 to 400 °C for up to 2 h) resulted in a significant increase in dye adsorption. After thermal exposure of STL to 300 °C for 1 hour, removal efficiencies of 98.8 % and 72.8 % were observed, respectively, for RG19 and RV5. Characterization of the adsorbent by TG/DTA and FTIR measurements showed that structural and chemical changes occurred in the lignocellulosic material which were probably responsible for the enhancement in adsorption capacity. These results strongly support the use of activated STL as a low-cost alternative to conventional adsorbents.

Reuse of Woody Biomass Fly Ash in Cement-Based Materials: Leaching Tests

The feasibility of using woody biomass fly ash (WBFA) as a mineral admixture in cement-based materials was investigated. This fly ash was characterized for chemical composition and used to prepare a cement blend with 70 wt% Portland cement and 30 wt% WBFA. Cubic specimens were cast from a blended cement paste (water-to-binder ratio 0.50) and, after 28 days of curing at 20°C and 100% relative humidity, these specimens were tested for heavy metal leachability through the use of a sequential leaching protocol, at a constant pH of leachant (deionized water; pH 6.0). It was found that, except for the chloride content, the WBFA is able to meet the European chemical requirements established for reuse of coal fly ash in cement-based materials. Although the WBFA is characterized by a significant content of heavy metals of particular environmental concern (Cd, Cr, Cu, Ni, Pb, Zn), the results of the monolith leaching test have shown a good immobilization capacity of such metals by the cementitious matrix and, consequently, a good environmental quality of the blended cement investigated.

Screening and Thermal Desorption for Remediation of a Sediment Polluted by the Mercury of a Chlor-Alkaly Plant

Thermal desorption tests were performed on samples taken from a mercury polluted sediment (133 mg/kg) in the vicinity of a chlor-alkali plant that has been operating over a long period using mercury cathodes. After characterization of the sediment, by means of TGA/DTA, SEM, XRD and chemical analysis, the material was screened into various size-fractions. Chemical analysis showed that only the finest size-fractions had a mercury content above the regulatory limit (5 mg/kg) established for areas destined for industrial installations. Thermal desorption tests were applied on the finest size-sediment fractions at furnace temperatures between 300°C and 400°C and solids residence times between 3 minutes and 120 minutes. After 3 minutes at 400°C, the treated sediment residue had a mercury content below the regulatory limit. The short solid residence time and the low desorption temperature required to meet the treatment standards would permit the use of a continuous thermal desorption treatment process in a rotatory dryer, providing that the values of residence times obtained by the lab-scale plant are suitable for a larger scale plant.

Utilization of automotive shredder residues in a thermal process for recovery of manganese and zinc from zinc–carbon and alkaline spent batteries

The aim of the study is the recovery by thermal treatment of manganese and zinc from a mixture of zinc-carbon and alkaline spent batteries, on the basis of the different phase change temperatures of the two metal-bearing phases. ASR (Automotive Shredder Residue), containing 68% of carbon, was added to the mixture to act as a reductant to metallic Zn of the zinc-bearing phases. The mixture was subsequently heated in different atmospheres (air, CO2 and N2) and at different temperatures (900°C, 1000°C and 1200°C) and stoichiometric excess of ASR (300%, 600% and 900%). Characterization of the mixture and of the residues of thermal treatment was carried out by chemical analysis, TGA/DTA, SEM and XRD. The results show that recovery of 99% of zinc (grade 97%) is achieved at 1000°C in N2 with a stoichiometric excess of car-fluff of 900%. This product could be suitable for production of new batteries after refining by hydrometallurgical way. Recovery of Mn around 98% in the residue of the treatment is achieved at any temperature and atmosphere tested with a grade of 57% at 900% excess of car-fluff. This residue is enriched in manganese oxide and could be used in the production of iron-manganese alloys.

Hyperspectral imaging based techniques in contaminated soils characterization

Contaminated soil characterization represents one of the primary key-factors to evaluate when reclamation strategies have to be designed and applied. Soil characterization are conventionally performed adopting integrated physical-chemical analyses based on soil portion (samples) directly collected in situ. Such an approach is obviously time consuming. In this work is examined the possibility offered by hyperspectral imaging based techniques to perform fast and reliable tests able to identify and quantify specific soil characteristics of primary importance in soil reclamation. The proposed approach, methodologically very simple to apply, for its flexibility could be profitably utilized also for other applications as those linked to agricultural soil monitoring.