Leaching Of Material Research Articles

Experimental study of accelerated leaching on hollow cylinders of mortar

Two mortars, differencing mainly in their initial porosity, were degraded by the use of a chemically accelerated process with ammonium nitrate solution. To specifically study the leached material, the chemical attack was undertaken on thin walled tubes. The leaching effects were evaluated by studying variations in mechanical and hydraulic properties. For both mortars tested, the kinetics of relative loss in strength, in elastic modulus and of increase in permeability were similar. For the same time of degradation, the increase in porosity and the loss in volumetric mass roughly depend on the estimated cement paste proportion of each mortar. The total process of degradation was carried out in three steps: 4, 8 and 16 days. Very sharp variations of all the studied properties were observed until 8 days of leaching followed by a plateau. These two phases are attributed to Portlandite dissolution first then to progressive C–S–H decalcification. At the end of the leaching test, a permeability increase of more than two orders of magnitude and a loss in strength and elastic modulus of more than 85% were observed for both mortars.

Trace elements and heating value from sewage sludge, Barueri, Sao Paulo, Brazil

The fate of sludge in rivers and streams is a problem because of large quantities produced by industrial and domestic processes in big cities. In the present work, sludge heating value and its chemical composition were studied to evaluate sludge reuse in agriculture or in some industrial processes or energy recovery. The leached material was chemically characterized by ICP‐OES (plasma emission spectroscopy), which indicated trace elements like Ba, Ce, Co, Cr, Cu, Ga, La, Nb, Nd, Ni, Pb, Zr, Zn, Y, V, U, Th, Rb, Sc, Sr, by X‐ray fluorescence (XRF), in which oxides were found. Its heating value was determined using bomb calorimetry.

Rate of Hydroxypropylation of Starches as a Function of Reaction Time

AbstractTo determine the course of the hydroxypropylation reaction as a function of reaction time, waxy corn, normal corn, potato, and wheat starches were reacted with propylene oxide under normal reaction conditions. Amounts of leached material and MS values of both leached and granular molecules were determined over the course of reaction. For waxy and normal corn starches, the extent of reaction increased linearly from 0 to 12 h, after which the reaction proceeded at an ever decreasing rate, reaching zero at about 30 h of reaction. The initial rate of reaction was determined by reacting waxy corn starch with a greater amount of propylene oxide (10×normal concentration) so that there would be no slowing of the reaction due to loss of reagent. Results confirmed that the initial reaction rate was linear. The hypothesis that, as derivatization proceeds, granules are opened up, resulting in ever increasing rates of reaction was not substantiated. Amounts and MS values of leached molecules from waxy and normal corn starches increased continuously over the course of the reaction. For potato and wheat starches, MS values of the granular starch also increased continuously over the entire reaction period. Amounts of leached molecules from potato starch were greater than those from wheat starch, with the amount leached at 30 h from potato starch being slightly more than that from normal and waxy corn starches and that from wheat starch being considerably less.

Evaluating Children's Health Risk from Exposure to Municipal Solid Waste Truck Leachate in the United States: Complementary Evidence-Based and Risk-Based Assessments

ABSTRACTThe general public is exposed to leached material from municipal solid waste (MSW) trucks on a daily basis and some of this waste may harbor human pathogens. Children may be especially susceptible to exposure to such waste due to behavior during outdoor play and perhaps due to greater susceptibility to infection. We assess the public health risk through exposure to leachate from MSW haulers in two ways: a review of literature dealing with worker exposure to waste and incidence of illness, and by a risk assessment of exposure to leachate from MSW trucks with loads containing diapers from children with active infections caused by Shigella or Salmonella. Infectious risk was evaluated by a Monte Carlo simulation of exposure via ingestion of one milliliter of MSW truck leachate. Forecast doses of pathogenic bacteria were compared to published values of infectious doses (N50). A low level of concern was found from exposure of the public to municipal solid waste leachate by either evidence-based evaluati...

Design and Construction of a Cell to Model the Stabilization of Toxic Waste Solids to Residuals by Means of an Encapsulated Process

The residuals from galvanization processes, production of electronic components, paintings, electroplating, steel production, etc., are considered dangerous due to their high content of heavy metals such as lead and chromium. In this work, we designed and built a quartz cell which is able to resist the high temperatures at which the cement type, Portland, is obtained, with the purpose of exploring the stabilization of these elements when incorporating them into the process of production of the cement, and evaluating various quantities added as ingredients. The influence of this addition in the primary product, the clinker, is evaluated, as well as the retention of the metals and their possible incorporation into the rotational oven. The clinker production process is simulated by coupling the cell built into a laboratory device mounted to model the process. Temperature is controlled and the heating ramps represent the real process of production. Tests of leached material were performed on the product, under the norm governed by the Environmental Protection Agency (EPA), to verify the incorporation and retention of the metals studied in the structure of the clinker. Compression tests were carried out to verify that the addition of the metals does not affect the mechanical properties of the final product. Samples were prepared by additions of from 5 to 20 wt% of each element and the clinkering process was simulated in a laboratory device. Leaching tests were performed with the produced clinker samples in order to verify the incorporation of the studied metals in the clinker structure and the 28‐day compressive strength test in order to verify mechanical properties of the product. Scanning electron microscopic analysis revealed the effectiveness of the encapsulation among the clinker crystalline phases. The results led to the conclusion that additions of up to 20 wt% of lead and up to 5 wt% of chromium to clinker raw‐material are totally incorporated and do not affect the maximum compressive strength.

Studies on the leaching behaviour of heterotrophic microorganisms isolated from an alkaline slag dump

Eleven heterotrophic isolates from an alkaline slag dump, including nine bacteria strains, one fungus and one yeast isolate, were investigated for their ability to leach alkaline siliceous material. The efficiencies of these isolates were compared with those of chemical processes. Under defined experimental conditions, all the organisms demonstrated leaching capability, but, in general, the bacteria were more effective than the fungus or the yeast. The bacteria strains leached up to 38% of the manganese and up to 46% of the magnesium and were more selective than chemical processes. Scanning electron microscopy (SEM) analysis of the solid material after leaching showed considerably more surface erosion of the biologically leached material than observed in the control experiments. The possible long-term risks originating from uncontrolled leaching in alkaline waste dumps, as well as the participation of microbial activity in weathering processes of mineral materials, are briefly discussed.

Simultaneous evaluation of composite biodeterioration and changes in the physicochemical and biological water characteristics

Biological factors in aquatic environments may accelerate the deterioration of composite material, while the leached material can adversely impact the surrounding ecosystem. The main objective of this study was to examine the interaction between physicochemical and biological characteristics of water and polymer composites, using four water-composite systems (distilled water with composite, river water, river water and composite, and river water plus composite and biocide). In distilled water, leaching of the composite coupon produced an increase in pH (11%); conductivity (30ppm); and total organic carbon (TOC) (31mg/l). Conversely, the presence of bacteria buffered river water pH. Bacteria in non-sterile reactors degraded the TOC leached from the composite, preventing its accumulation. However, this led to higher oxygen demands which were also indicated by increasing bacterial numbers in the three non-sterile water systems. Exposure to river water over 12 months produced an 11% reduction in the tensile modulus of composites; almost twice that for the distilled water and the system containing biocide. Biocide did prevent the tensile modulus reduction, but led to 28mg/l TOC accumulation. Visual observations corroborated the observed differences. Craters and precipitates, exposed fibres, and material debonding were observed on the coupon surface. For the river water system, biofilm growth was also observed. The presented study provides a useful and preliminary database for physicochemical and biological characterization of water interacting with deteriorating polymer composites.

Synthesis of skeletal silver from rapidly solidified Al–Ag precursor

Skeletal silver was synthesized by applying an alkaline leaching process to rapidly solidified Al–Ag granular precursors. The structure of the leached materials was examined by scanning electron microscopy, EPMA, X-ray diffraction and differential scanning calorimetry. Most of the aluminum was leached out and only a few percent aluminum remained in the as-leached state. The crystallographic structure of the leached material was face centered cubic and it was formed by rearrangement of silver atoms dissolved in the α-Al solid solution during leaching. The Ag 2Al phase was too stable for the alkaline solution so that it did not contribute to the formation of skeletal silver. The formation ratio of skeletal silver to the total silver in the precursor depended on the amount of dissolved silver in the α phase. Rapid solidification of Al–Ag alloys was quite effective for obtaining the super-saturated α phase. More than 80% of the silver in the precursor turned into skeletal silver using the rapidly solidified precursor. The specific surface area of the skeletal silver was about 9 m 2/g. The mean diameter of the skeletal silver was about 20 nm as derived using the X-ray line broadening method. This value was 1.2–1.5 times smaller than that evaluated from the specific surface area assuming spherical silver particles. The difference may result from shape degeneration.

Effect of leaching on the ash behavior of olive residue during fluidized bed gasification

Fluidized bed gasification is considered to be the most advanced method for thermochemical conversion of various biomass fuels, e.g., wood, energy crops, agroresidues, etc., to energy offering economical and environmental benefits. Ash-related problems including sintering, agglomeration, deposition, erosion and corrosion resulting due to the low melting point ash of agroresidues are the main obstacles for economical and viable application of this conversion method for energy exploitation of the specific residues. The effect of leaching (washing) the olive residue in order to improve its ash thermal behavior under the gasification conditions was studied. Gasification tests were performed in a lab scale fluidized bed gasifier with both leached and non-leached samples and the results concerning the ash thermal behavior of the used samples were associated with their ash elemental analysis, while the deposits produced during the gasification tests were analyzed using SEM-EDX analysis technique. The produced results clearly show that leaching could help significantly in avoiding to a great extent, the operational problems associated with the problematic ash thermal behavior in the case of olive residue. In particular, all gasification tests performed using the non-leached olive residue material as feedstock resulted in a rapid agglomeration of the reactor's bed material and consequently to the end of the gasification tests. On the contrary, gasification tests performed using the leached olive residue material ended without any agglomeration-deposition problems, while the operation time was in all cases longer compared with the tests with the non-leached olive material.

Mechanical properties of calcium-leached cement pastes: Triaxial stress states and the influence of the pore pressures

Application of concrete in nuclear waste containments requires knowledge of its mechanical behavior when subjected to calcium leaching. In order to address real-life situations, multiaxial stress states of leached material must be considered. This paper reports results from a series of triaxial tests of calcium-leached cement paste obtained from accelerated leaching tests that operate on an acceleration rate of 300, compared with natural calcium leaching. Along with the global strength loss due to chemical decohesion, an important loss of frictional performance is reported. Environmental scanning electron microscope (ESEM) pictures of both leached and unleached material are presented, and they indicate that this loss of frictional performance can be associated with a highly eroded microstructure perforated by the leaching process. In addition, the frictional behavior of leached cement pastes is found to be strongly dependent on the drainage conditions of the material and thus, on the interstitial pore pressure. Through a poromechanical analysis, it is shown that this high pore pressure sensitivity of leached cement paste can be attributed to the low skeleton-to-fluid bulk modulus ratio, K s/ K f, of the degraded material, which, together with the increase in porosity, leads to the high compressibility of calcium-leached materials. This low K s/ K f ratio is the consequence of an intrinsic chemical damage of the solid skeleton, which occurs during calcium leaching.

Evolution of sulphides-rich mine tailings and immobilization of As and Fe

Since large areas have been contaminated by mining activities, knowledge about the evolution of polluted sites and pollutant speciation are required for environmental risk assessment. A mineralogical and chemical investigation was performed on the site of the Cheni's mine (France), where sulphide-rich tailings, containing large amounts of arsenic (As), were abandoned in 1944. It revealed that most of S, Fe and As are no longer in sulphide forms in the surface layer (0–2 m). Oxidation products are gypsum, epsomite and As-rich Fe hydroxides. Arsenic fixation was found to be reversible when leaching conditions increase. We also attempted to provide an approach of the As-bearing phases using a normative calculation: average composition is [Fe 2O 3] 5[As 2O 5] 4·30 H 2O nearby the reduced original material, and [Fe 2O 3] 3[As 2O 5]2·18 H 2O in more leached material.

Micromorphological indications on the nature of the Late Quaternary Paleosols in the southern coastal plain of Israel

The nature of alternating layers of clayey soil material and calcareous soil material in the desert fringe area is discussed. In earlier work by other researchers, these soil materials were considered as representing different climatic environments: the clayey layers a wet period and the calcareous layers a dry period. Based on a pedogenic approach supported by micromorphological indications, however, it is concluded that the clayey layers together with the calcareous layers form a single pedogenic unit developed in the same climatic environment. The calcareous layers are in fact calcic horizons accumulated from the overlying leached clayey material and their appearance is similar to the modern Brown Grumusolic soils that occur in the semiarid area of the coastal plain. A sequence of four superimposed Brown Grumusolic paleosols, developed during the last glacial period, was recognized. In the western part of the coastal plain, Quartzic Brown soils and Husmas soils which developed on sand dunes occur. The former has an argilic horizon with a calcic horizon below. Microcalcites of eolian dust origin are homogeneously distributed in the plasma, the soil representing a monogenetic soil type developed during a semiarid climate. The latter is a Reddish Brown Mediterranean polygenetic soil with leached soil material, in which the calcic horizon accumulated from a loessial soil cover that settled during a drier climate. Both soils also developed during the last glacial period. In the eastern coastal plain, older paleosols which developed on sand dunes occur below the Brown Grumusolic soils. One type is a polygenetic leached Quartzic Gray Brown paleosol, not recognized in previous studies, which overlies a Red Hamra soil (sandy Red Mediterranean soil).

+The effect of amylose–lipid complex formation on enzyme susceptibility of sago starch

Native sago starch was incubated at 60°C with lysophosphatidylcholine, monomyristin, monopalmitin, and monostearin. Differential scanning calorimetry peaks centred at 100–120°C indicated formation of amylose–lipid complexes. Among the four lipids, lysophosphatidylcholine showed the highest complexing ability, while that of the monoglycerides decreased with the increasing chain length. Part of the amylose leached during the incubation, and the amount of leached material decreased in the presence of lipids. Starch–lipid samples were subjected to enzyme hydrolysis by porcine pancreatic α-amylase. The bioavailability of native and freshly gelatinised sago starch was decreased in the presence of lipids, while retrograded starch–lipid samples showed higher digestibility than starch control. ©

Rate of Ingestion and Proteolytic Activity in Digestive System of Juvenile White Shrimp, Penaeus vannamei, During Continual Feeding

ABSTRACT Juvenile white shrimp, Penaeus vannamei, were studied using tray feeders in relation to food ingestion and enzymatic activity, with data taken every two hours for five days. The feed ingestion was calculated by subtracting the uningested and the leached material from the food provided. Significant differences (P < 0.05) in the ingestion rate were found during the experiment. The greatest ingestion occurred between 2000 and 2200 hours. The largest feed ingestion coincided with the nocturnal activity of shrimp. Time-series analysis showed a cycle of increased ingestion before midnight and lower ingestion during daylight. Total protease, trypsin, and chymotrypsin activity were measured during the last 24 hours of the study and included both fed and starved organisms. The enzymatic pattern was similar for both groups. There was a decrease of the protease and trypsin activities before and after 1800 hours, just before the ingestion increased. The study of digestive enzymes provided evidence of a close association between behavior and regulation of the digestion system physiology. The results give some clues toward better feeding regimens and the use of feed management for continual monitoring of ingestion to get reliable evaluations for food conversion index. Feed management with tray feeders will reduce pollution in extensive ponds by decreasing the uningested food.

Toxicity studies on native Procion Red HE-3B and released dye from affinity material exposed to degradative chemical conditions

Leached ligands from chromatographic packing material submitted to drastic regeneration conditions can contaminate pure biological preparations. These contaminants could have adverse effects from a toxicology point of view that are very poorly documented in liquid chromatography for protein separation. Investigations on toxicity level have been made on released material from immobilized Procion Red HE-3B, after formal identification of the nature of the leached chemical material. Toxicity investigations in vitro involved a number of tests on living cells (eucaryotic and procaryotic) covering different aspects. Behaviour of cells in regular cultures, polyploïdia induction, genotoxicity as well as mechanisms of endocytosis have been studied. Results showed no toxic effects within the range of concentration of dye and dye derivatives studied. Genotoxicity studies in particular did not show any toxic effect over a range of concentration much higher than the regular level of dye leakage from the sorbent.

A concept of Gleyization and its role in the pedogenesis

Three simple factors ‐ excessive moistening, anaerobic microflora and organic matter, are indispensable and sufficient conditions for gley formation. This process is always characterised by a non‐silicate iron loss from the soil fine earth or soil plasma. Gley formation takes place under conditions of stagnant or stagnant‐percolative water regimes. In the second case gley formation induces a drastic acidification of the mineral soil part, lessivage, removal of iron, aluminium, calcium, magnesium, bleaching of the soil fine earth, and it appears the features of soil with eluvial, acid, bleached horizons. Therefore soils with such horizons should be regarded as manifestations of gley formation in conditions stagnant ‐percolative water regime on acid, neutral or leached parent material. Under influence of stagnant water regimes Fe of mineral substrat is removed and unconsiderable eluviation of Ca and Mg takes place. pH of parent material does not change or has the trend to increase. In this case does not arise a soil with bleached horizons.

Distribution of uronate residues in alginate chains in relation to alginate gelling properties — 2: Enrichment of β- d-mannuronic acid and depletion of α- l-guluronic acid in sol fraction

Alginate, a copolymer comprised of β- d-mannuronic and α- l-guluronic acid isolated from seaweeds and extruded by certain bacteria, forms a gel in combination with several divalent cations. Polymer chains leaching out at 7°C, 24°C and 50°C from Ca-, and Sr-alginate gel beads were found to be depleted in α- l-guluronic acid and enriched in β- d-mannuronic acid compared to the starting material. For Sr gels, leached material is found to be almost devoid of α- l-guluronic acid triplets for the Sr gels, and a significant reduction in such triplets compared to the starting material was observed for the polymers leached from the Ca-gels. The leached material was also found to comprise the low-molecular-weight tail of the starting material molecular weight distribution, the truncation towards lower molecular weight was larger for the more block-like alginate. The chemical composition of the leaching out from Sr-gels and Ca-gels suggests that 3 and 8 ± 2 contiguous α- l-guluronic acid residues are required to form stable junction zones for Sr- and Ca-induced gelation respectively.

Characterization and sintering of a porous glass-ceramic in the system Na2O-B2O3-Ta2O5

Substitution of SiO2 in the ternary sodium borosilicate system with Ta2O5 was found to produce glasses, which after heat treatment separated into immiscible microphases, one of which was water soluble. The structure of the leached material after heat treatment was a well developed low temperature form of Ta2O5. After firing at temperatures between 1100 and 1550°C X-ray diffraction analysis showed the presence of low and high temperature forms of Ta2O5 and of orthorhombic Na2Ta5O21. The high solubility of up to 40 wt% Ta2O5 in the sodium-borate matrix resulting in clear glasses is of practical interest. The specific surface areas of the leached materials ranged between 5.54 and 35.57 m2g−1 while in an additionally Al2O3 doped material the value of 307 m2g−1 was measured. Mean pore radii of interconnected pores were calculated to be between 18.63 to 41.12 nm in the Ta2O5-rich materials while the additional Al2O3 doping decreased the value to 2.71 nm. A sintering temperature between 1500 and 1550°C is estimated from void volume measurements after a series of firing steps at temperatures between 1100 and 1550°C were undertaken.

Improvements to Raney copper methanol synthesis catalysts through zinc impregnation: I. Electron microprobe analysis

The specific activity of a Raney Cu-ZnO-Al 2O 3 catalyst for methanol synthesis from carbon monoxide and carbon dioxide has been found to be related to the mass of zinc per unit total area of Raney catalyst surface. This correlation hag been found to be independent of the conditions used to leach the material, although the level of zinc was found to be strongly dependent on the leaching conditions. The mass of zinc oxide in the catalytic material produced by leaching a Cu-Al-Zn alloy pellet in sodium hydroxide has been found to decrease continuously from the highest level close to the alloy/catalyst interface to the lowest level at the outer edge of the leached pellet. By leaching the alloy in a zincate rich solution the ZnO concentration profile in the leached material Cu-Al-Zn alloys can be unproved. The resulting catalysts have significantly higher specific activity which shows a strong correlation to the mass of zinc per unit total surface area. The zincate leached materials were found to have total amounts of zinc similar to the hydroxide leached materials. However, the aluminium levels were significantly lower. The high specific activity was attributed to improved contact between the copper and the ZnO which is precipitated onto the copper surface. On the basis of these results it is suggested that the active sites for methanol synthesis are at the interface between the copper and the ZnO crystallites.

Lysimeter experiments on bentazon

The leaching behaviour, distribution, and metabolism of the herbicide bentazon within two years following application was investigated by a lysimeter study with undisturbed soil monolith and using the radiolabelled compound. This was achieved by analyzing compounds appearing in the leachate as well as analyzing radiolabelled residues distribution in the 1 m soil profile and in plants. Within the two years study less than 4 % of the applied amount of radioactive material occured in the leachate. The leached material, however, contained only minor amounts of bentazon. 0.03 % of the applied active ingredient reached the level below 1 meter. Only minor amounts of bentazon could be detected in the different soil layers two years after application, thus bentazon does not tend to accumulate in soil and does not move to deeper soil zones or groundwater. The uptake by plants amounted to 0.9% of the originally applied active ingredient. Approximately 50 % of the applied radioactive material had left the system within the two years. These losses might account for volatilization and/or mineralization processes.