High Leaching Rate Research Articles

Bioleaching of metals from electronic scrap by moderately thermophilic acidophilic bacteria

The present work was aimed at studying the bioleachability of metals from electronic scrap by the selected moderately thermophilic strains of acidophilic chemolithotrophic and acidophilic heterotrophic bacteria. These included Sulfobacillus thermosulfidooxidans and an unidentified acidophilic heterotroph (code A1TSB) isolated from local environments. Among the strategies adapted to obtain enhanced metal leaching rates from electronic scrap, a mixed consortium of the metal adapted cultures of the above-mentioned bacteria was found to exhibit the maximum metal leaching efficiency. In all the flasks where high metal leaching rates were observed, concomitantly biomass production rates were also high indicating high growth rates. It showed that the metal bioleaching capability of the bacteria was associated with their growth. At scrap concentration of 10 g/L, a mixed consortium of the metal adapted cultures was able to leach more than 81% of Ni, 89% of Cu, 79% of Al and 83% of Zn. Although Pb and Sn were also leached out, they were detected in the precipitates formed during bioleaching.

Leaching of neptunium from garnet- and murataite-based ceramics

Leach resistance of neptunium-doped garnet- and murataite-based ceramics with calculated compositions (in wt.%: 38 Fe2O3, 21 Gd2O3, 16 NpO2, 15 ZrO2, 10 CaO and 55 TiO2, 10 Mn2O3, 10 CaO, 10 NpO2, 5 ZrO2, 5 Al2O3, 5 Fe2O3 respectively was studied. The samples were prepared from pre-activated oxide mixtures by sintering/melting in platinum ampules at 1450 °C. The murataite ceramic is composed of predominant murataite structure phases with five- (5C) and eight-fold (8C) elementary fluorite unit cell and minor rutile (≤5% of total bulk). The garnet-based sample is a polyphase ceramic and consists of major garnet phase, interstitial Fe2O3 and Ca-Fe-phase, and rare grains of (Ca,Zr,Np)O2-phase (cubic solid solution) included in the larger garnet grains. The edge of the garnet grains is enriched with Np as compared with their rim by approximately 1.5−2 times. Np leach-rates were measured using an ANS_16.1 test. Np leach rate from the murataite-based ceramic reduced significantly from 2.44×10-6 g/(cm2 day) within the first 2 hours of leaching to 3.41×10-9 g/(cm2 day) at 672 hours of leaching. At the same time for the garnet-based ceramic corresponding values were 1.49×10-5 g/(cm2 day) and 1.77×10-6 g/(cm2 day), respectively. Higher leach rates at early periods are due to the dissolution of trace phases and Np release from defect surfaces. Leach rate values at later periods of leaching are characteristic of the “equilibrium” leach rate of the element (Np). Much higher Np leaching from the garnet ceramic may be due to 1) higher concentration of Np at the edge of the garnet grains with a relatively low chemical durability; 2) leaching of Np traces from highly soluble minor Np-Zr-rich phase.

The chemical composition of throughfall beneath oak, birch and pine canopies in Northwest Germany

The chemical composition of rainwater is altered upon its passage through tree canopies. In order to investigate how rainwater chemistry is affected by canopy-dependent processes in characteristic forest types of Northwest German sandy lowland regions – oak–birch-forests, Betula pubescens Ehrh. swamp forests, and stands of Pinus sylvestris L. – comparative studies on the chemical composition of throughfall were carried out at seven forest sites, situated in close proximity within a nature reserve. Additionally, rainwater was sampled at three heathland sites for analysis of open-field precipitation and at three sites along an oak–birch-forest edge. Throughfall concentrations of most of the parameters analysed were significantly higher than open-field concentrations, especially with regard to electric conductivity, NH4-N, K+, and KMnO4-index. Ion concentrations in throughfall were the lowest in a 10-year-old stand of Betula pendula Roth. and Pinus sylvestris and in a Betula pubescens swamp forest and were highest beneath a stand of Pinus sylvestris. Except for Na+, Cl−, and NO 3 − , ion concentrations in both throughfall and open-field precipitation increased during the growing season (May–October). In throughfall, Ca2+, Mg2+, K+, and Mn2+ were strongly correlated. Enrichment ratios between throughfall and open-field deposition varied among sites and elements and were the highest for K‰+, Mg2‰+, and Mn2‰+. Estimates of canopy leaching indicated high leaching rates of K‰+ and Mn2‰+ and moderate leaching of Mg2‰+. The contribution of foliar leaching to throughfall deposition was higher at the deciduous than at the coniferous stands.

A comparison of the kinetics and mechanism of acid leaching of sphalerite containing low and high concentrations of iron

The leaching behaviour of three Fe-containing sphalerite minerals (0.45, 11.40, and 12.90 wt.% Fe) was investigated at pH 1 in O 2-purged HClO 4 from 25 to 85 °C. For all three sphalerite samples, the leach data closely fitted a rate expression which incorporates both a shrinking sphere term and rate control via diffusion through a reacted surface layer. The leach rate increased with increasing Fe content of the sphalerite. At 85 °C after 168 h of leaching, 0.89 of the Zn had been leached from the 12.90 wt.% Fe-containing sphalerite while, over the same period of time, 0.49 of the Zn had leached from the 0.45 wt.% Fe-containing sphalerite. The activation energies for leaching decreased with increasing Fe content of the sphalerite (i.e. for Zn leaching 63±6, 50±7 and 39±2 kJ mol −1 for the 0.45, 11.40 and 12.90 wt.% Fe-containing sphalerite samples, respectively). The activation energy of leaching of Fe and Zn was within experimental error for the 11.40 and 12.90 wt.% sphalerite samples. The solution Fe content was not measured reliably for the 0.45 wt.% Fe-containing sphalerite. The leaching mechanisms have been interpreted as a function of surface speciation, which was analysed using time of flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) for samples leached at 85 °C. The decrease in Zn dissolution rate on leaching is attributed to the formation and growth of a polysulfide surface layer, which forms during the initial rapid leach period. The formation of elemental sulfur during the subsequent slow leach period does not further affect the leach rates. The concentrations of polysulfide and elemental sulfur that form increase with increasing Fe concentration as expected from the higher leach rates. The formation of polysulfide and elemental sulfur on the ZnS surface consumes H + (via conversion to H 2O) thus decreasing solution acidity.

Simulation of nitrate leaching for different nitrogen fertilization rates in a region of Valencia (Spain) using a GIS–GLEAMS system

Abstract The groundwater loading effects of agricultural management systems (GLEAMS) model coupled to a GIS was used to evaluate the effect of different fertilization treatments on the total N leaching in a selected area of eastern Spain with intensive agriculture. Four nitrogen fertilization rates (traditional or base, base rate reduced by 20%, reduced by 50%, and the rate calculated by the Nmin recommendation system for vegetables, and reduced by 70% for citrus) were evaluated at a regional scale to find the rate that minimized N leaching without reducing crop N uptake. Nitrate leaching maps were obtained for the different nitrogen rates studied. A great reduction of N leaching (up to 68% for vegetables, and 75% for citrus) was observed under the most reduced fertilization rates and this reduction was greater in areas irrigated with surface water in comparison to those irrigated with groundwater. The GIS–GLEAMS system was a useful tool to assess the N leaching at a regional scale for the different N management considered. For example, it was shown that the Nmin recommendation system was the most efficient for vegetables, and for citrus the most efficient fertilization rate was the reduced 50%, that is similar to that recommended by the Code of Good Agricultural Practices. The areas irrigated with groundwater with high nitrate content had a high leaching rate, and the nitrate applied in irrigation water should be considered when planning the crop fertilization. A temporal analysis of the NO3-N in soil, N leaching, crop evapotranspiration and rainfall allowed to identify the influence of the soil NO3-N and the rainfall on nitrate leaching.

Nitrate and pesticide contamination of groundwater under rice-based cropping systems: past and current evidence from the Philippines

The quality of shallow groundwater used for domestic purposes by the rural poor in developing countries is threatened by contamination with nitrate and residues of pesticides used in agriculture. In Asia, many of the rural poor live in rice-producing areas where the continuous flooding of rice ( Oryza sativa) fields may lead to high leaching rates of groundwater contaminants. This study presents results of measurements of nitrate and pesticide concentrations in shallow groundwater in 54 domestic wells under rice-based production systems in Luzon, Philippines, from 1989 to 2000. In irrigated double rice cropping areas, seasonal-mean nitrate concentrations were 0–2 mg l −1, which is below the WHO limit of 10 mg l −1 for drinking water. In wet season (WS) rainfed rice and dry season (DS) irrigated sweet pepper ( Capsicum annuum) double cropping areas, monthly mean nitrate concentrations were 5–12 mg l −1. Nitrate concentrations were lower under other, less fertilized upland crops, and with a high percentage of the area under rice in the WS. Mean pesticide concentrations were generally one to two orders of magnitude below the WHO single (0.1 μg l −1) and multiple pesticide (0.5 μg l −1) limits, although temporary peak concentrations of 1.14–4.17 μg l −1 were measured. For both nitrate and pesticides, the high leaching potential appears to be offset by the particular transformation and loss processes taking place under tropical, anaerobic conditions. The agro-ecological environment and history of the study sites suggest that the results may be characteristic of many parts of tropical Asia where rice-based cropping has intensified since the Green Revolution in the mid-1960s.

Effectiveness of commercial reagents for heavy metal removal from water with new insights for future chelate designs

Toxic heavy metals in air, soil, and water are global problems that are a growing threat to the environment. To meet the federal and state guidelines for heavy metal discharge, companies often use chemical precipitation or chelating agents. In order to be competitive economically, many of these chelating ligands are simple, easy to obtain, and, generally offer weak bonding for heavy metals. Laboratory testing of three commercial reagents, trimercaptotriazine (TMT), Thio-Red ® potassium/sodium thiocarbonate (STC), and HMP-2000 sodium dimethyldithiocarbamate (SDTC) has shown that the compounds were unable to reduce independent solutions containing 50.00 ppm of divalent cadmium, copper, iron, lead, or mercury to meet EPA standards. Additionally, the compounds displayed high leaching rates and in some cases decomposed to produce toxic substances. In contrast, the studies demonstrate that a recently reported sulfur-containing multidentate ligand is both safe and effective for the removal of these metals.

Some properties of a lead vanado-iodoapatite Pb 10(VO 4) 6I 2

A lead vanado-iodoapatite Pb 10(VO 4) 6I 2 was synthesized as a potential waste form to immobilize radioactive iodine and some thermal, mechanical and chemical properties were measured. Thermogravimetry–differential thermal analysis (TG–DTA) showed that the apatite was stable up to about 800 K. The thermal conductivity of the hot-pressed sample, with the theoretical density of 82%, increased gradually with increasing temperature from 0.65 W m −1 K −1 at room temperature to 0.78 W m −1 K −1 at 523 K. The micro-Vickers hardness and Young's modulus were lower than those of a typical glass waste form. The leaching rate of iodine for apatite was two orders of magnitude higher than that of an AgI glass waste form. Despite the high leaching rate (compared to AgI embedded in glass), the high chemical stability up to 800 K and acceptable mechanical properties of this apatite suggest that it will be a good waste form when embedded in a suitable matrix material.

The cyanide leaching of gold in solutions containing sulfide

A large proportion of the gold processed in the 21 st century will be recovered from sulfide ores. Since the sulfide minerals are to some extent soluble in cyanide solutions, there will always be some sulfur species present in the leach solution. It has been shown that soluble sulfide hinders the rate of gold leaching, forming a protective layer of the type Au/S x. Electrochemical studies of the constituent half reactions: gold oxidation; and oxygen reduction, were consistent with this view. The effect of sulfide and cyanide concentrations on the leaching reaction were investigated, and it was shown that the sulfur formed is chemically attacked by cyanide, resulting in higher leach rates at higher cyanide concentrations. The effect of lead was also studied and is discussed in detail.

Bioleaching of a Spanish complex sulphide ore bulk concentrate

In the present work the applicability of bioleaching using a mixed culture of mesophilic microorganisms (Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Leptospirilum ferrooxidans) on a bulk concentrate of a Spanish complex sulphide ore was studied. The bulk concentrate mainly consisted of by chalcopyrite, sphalerite and pyrite. Effects of nutrient medium, stirring, pulp density, temperature and the addition of CO 2 (1% v/v) to the air flow were also studied. The highest leaching rates and recoveries were obtained with mechanically stirred reactors at 5% pulp density and 9K medium. However, by using 9K medium higher jarosite precipitation was observed. Results showed that the optimum temperature for copper bioleaching was 30°C, whereas zinc dissolution increased with a rise in the temperature.

Nutrient leaching and end product accumulation in plastic composite supports for L-(+)-lactic Acid biofilm fermentation

Investigations on the leachate bioavailability, leaching rate, and lactic acid accumulation properties of plastic composite supports (PCS) were essential for large-scale or long-term lactic acid fermentation. Leachates from PCS and polypropylene discs (controls) were analyzed by the micro-Kjeldahl method; by absorbances at 260, 275, and 280 nm; and by bioassays with Lactobacillus casei subsp. rhamnosus (ATCC 11443). The amount of leached nitrogen in a 20-ml initial soaking solution had a high correlation with the soaking solution's cell density (r = 0.87) and absorbance at 260 nm (r = 0.95). Leaching rates of various PCS were evaluated by 20 20-ml simulated repeated-batch fermentations (RBF). PCS with only yeast extract as the minor agricultural ingredient had a high leaching rate and leached out 51 to 60% of the total nitrogen during the first RBF. PCS blended with dried bovine albumin, dried bovine erythrocytes, and/or soybean flour had slowed nutrient leaching (20 to 30% of the initial leached nitrogen). Hence, they could still maintain 1 g of lactic acid per liter and measurable cell density (absorbance at 620 nm, 0.4 to 0.6) at the 20th 20-ml RBF. Lactic acid accumulation properties of PCS were evaluated by soaking the supports in a 30% lactic acid solution for 72 h at 45(deg)C. The lactic acid-soaked supports were rinsed three times and then heat treated (121(deg)C, 15 min) in 15 ml of deionized water. The results showed that lactic acid accumulation in PCS was mainly due to absorption and had no correlation with lactic acid production or biofilm formation.

Organic Phosphorus in Solutions and Leachates from Soils Treated with Animal Slurries

AbstractA substantial part of the total phosphorus (P) in soil solution and leachates can be present as dissolved organic phosphorus (DOP). The DOP may be more mobile than inorganic orthophosphate and thus it can be an important P source for surface water eutrophication. This paper describes a series of four experiments that investigated the effects of animal waste application to sandy soil on DOP leaching. The first experiment examined the effect of storing pig slurry on DOP fractionation, using gel permeation chromatography. Experiment two and three examined the immediate and long‐term effects of animal waste application to soil in laboratory columns and outdoor maize‐grown lysimeters, respectively. In the fourth experiment concentrations of DOP and total P (TP) in soil solutions at various depths were determined in a long‐term field experiment. Results indicate that DOP in pig slurry is mainly found in high molecular weight (MW) compounds (Exp. 1). From the soil column more than 90%, and from the lysimeters more than 70% of TP leached as DOP (Exp. 2 and 3). In the lysimeter experiment (Exp. 3), leaching of TP mainly occurred in periods of low Cl and NO3 concentrations, induced by high leaching rates. This may indicate that P transport in these periods was mediated by DOC or other colloidal particles. The field experiment (Exp. 4), showed that DOP as a percentage of TP in the soil solution increased from about 10% in the topsoil to more than 70% at 70 to 80 cm depth, which was mainly due to a decrease in MRP. Thus, DOP is an important form of P in leachates and in soil solutions in the subsoil, and characterization of this DOP can improve our understanding of P leaching from soils.

Elemental dynamics of a Japanese watershed with sugi (Cryptomeriajaponica) and hinoki (Chamaecyparisobtuse) plantations

The roles of various components of the biogeochemical cycle in contributing to elemental loss or retention were evaluated in a Japanese watershed with 18-year-old plantations of sugi (Cryptomeriajaponica) and hinoki (Chamaecyparisobtusa). There was a large amount of foliar biomass (24.1 Mg•ha−1), which induced a large net increase of K+ (20.4 kg•ha−1•year−1) and consumption of H+ (0.26 kg•ha−1•year−1) in the canopy. Most of K+ in throughfall + stemflow was retained by vegetation increment. Although vegetation increment of N (33.9 kg N•ha−1•year−1) was larger than bulk precipitation N input (10.4 kg N•ha−1•year−1), high drainage loss of NO3− (13.6 kg N•ha−1•year−1) was observed. High N-mineralization and nitrification rates were suggested by high concentration of soil solution NO3− (315–434 μequiv.•L−1) and small forest floor N content. The high leaching rates of NO3− contributed to the high loss rates of Ca2+, the dominant cation in soil solution. The high N-mineralization and nitrification rates were likely due to the high temperature and moisture as well as the historical management of the watershed. High temperature and abundant moisture also accelerated chemical weathering of plagioclase, resulting in high drainage losses of HCO3−, Si, and Na+ and consumption of H+.

Developments in evaluating environmental impact from utilization of bulk inert wastes using laboratory leaching tests and field verification

In recent years leaching tests for construction materials and wastes have been developed with the emphasis on using them as prediction tools for release in the long term rather than as arbitrary pass/fail tests. In the first stages of development, the mechanisms of release and release-controlling parameters have been assessed. For each of these aspects leaching tests have been selected, developed and in part standardized. Not all relevant aspects of leaching are yet covered. The reducing properties of materials, for example, are still not taken into account properly. The need for these more elaborate tests is increasing as the policy of re-using waste materials in construction is expanding. As a consequence, the desire to improve material quality is increasing. For this purpose more detailed knowledge on the chemical speciation of contaminants is needed, as a treatment of waste carried out to reduce a few contaminants with too high leach rates may lead to an undesired increase in the release of other contaminants, which were previously not a problem. This requires a more integral approach and a good understanding of the consequences of changes in material properties. Tests focused on two main aspects of leaching can be identified: (1) release as a function of time; (2) release as a function of main leaching controlling parameters, such as pH, redox and complexation. The relation between these tests and the data interpretation associated with them is discussed. Another distinction in the use of tests is related to the level of understanding needed. In CEN TC 292 tests have been distinguished as: characterization tests, compliance tests, and on-site verification tests. An important aspect of the new development of tests with release prediction capabilities is the verification of such predictions in the field. An example of the relation between predictions of release from laboratory test data and field observations is presented: release from MSWI bottom ash monofills. Finally, recent developments in the EC DGXII Standard, Measurements & Testing Programme and CEN TC 292 Characterization of Wastes are addressed.

黄銅鉱浮選精鉱のバクテリアリーチングに及ぼす銀イオンの影響

It is known that the addition of silver ions enhances the bacterial leaching of chalcopyrite. This paper evaluates the influence of several factors, such as initial pH, silver concentration, the kind of silver compounds added, and the procedure of silver addition, on the catalytic effect of silver ions in bacterial leaching of chalcopyrite flotation concentrate using Thiobacillus ferrooxidans. To avoid the inhibition of growth of T. ferrooxidans by silver ions, the inoculation was carried out after 90 minutes of silver addition as silver sulfate solution. The leaching rate of copper at the initial stage of experiments increased with increase in initial silver concentration. The increase in the yield of copper leaching leveled off after the bacterial leaching of about 15 days, but adding silver ions again activated the leaching of copper. The highest leaching rate and the recovery of copper were obtained in the experiment carried out at the initial pH of 1.3. The catalytic effect of silver ions was not observed at the initial pH of 1.0. When silver ions were added after 10 days of inoculation, higher yield of copper leaching was obtained compared to the experiment with the silver addition at the beginning. The addition of silver sulfide powder also accelerated the bacterial leaching of chalcopyrite.

Water extractable organic matter in arable soils: Effects of drought and long-term fertilization

The concentration of water extractable organic carbon (WEOC) was determined over 2 yr at three different depths from three agricultural fields, which have been used for fertilization productivity studies for over two decades. The overall mean value for all samples was 9.40 μg WEOC g −1. The use of mineral fertilizer alone had no significant effect while organic fertilizer resulted in an overall increase of 15 ng WEOC g −1 (soil dry weight basis) or 220 g WEOC ha −1 per 1 kg N ha −1 yr −1 . This increase was usually non-linear for any given field or depth. Water flow appeared to play a role in that the deepest samples (60–90 cm) from the field with the highest leaching rate had consistently low WEOC values. The samples taken in a year (1991) with exceptionally low precipitation before sampling had significantly ( P < 0.001) more (+33%) WEOC than in the other year. The magnitude of this effect was equivalent to that of the application of organic fertilizer at the rate of ca175 kg N ha −1 yr −1. Therefore, in situ soil moisture content can have a relatively high effect on this organic carbon pool. Surprisingly the increase in WEOC due to drought was also present in the samples from the greatest depth. Again the field with the highest leaching rate was affected differently than the other two fields. No relationship was found between short term organic carbon mineralization and fertilization history. However, a significant but loose ( R 2< 50%) linear relationship was found between the mineralization rate and WEOC concentration.

The dissolution of biotite single crystals in dilute HNO 3 at 24°C: Evidence of an anisotropic corrosion process of micas in acidic solutions

The aim of this study is to determine the geometrical parameters which influence the dissolution of phyllosilicate crystals. In order to explain the natural transformations of phyllosilicates, like biotite, it is important to have a realistic measure of their reactive surface area. The present investigation is performed on sized biotite single crystals (Bancroft, Ontario). Batch experiments are performed at 24°C and in 0.1 N HNO 3 ( pH = 1.08 ± 0.02) in order to avoid the effect of hydroxide precipitates. Experiments are designed so as to determine the respective contributions of the two types of geometric interfaces between the biotite crystal and solution: 1. (1) external (001) planes of the crystal (surface area [S]), and 2. (2) lateral surface (surface area [SL]). The latter parameter is difficult to measure and the influence of [SL] is accessible in experiments where the mass or the perimeter of the monocrystal is varied while other parameters remain constant. The measure of the concentration of leached cations in solution and the investigations performed on the solid show the preponderant influence of [SL] on the corrosion process. On the external (001) interfaces, dissolution is only localized around defects that have the shape of lines or circles. The dissolution of biotite in 0.1 N HNO 3 is selective. The decreasing order of leaching rates for short runs is Mn > K > Al, Fe> Mg, Ti > Si. Fast ion exchange with H + accounts for the high initial leaching rate of the interlayer cation, K +. The fast initial release of Al with respect to Si is consistent with well established models of the surface chemistry of oxides. For octahedral cations, such understanding is still not possible and we could only present some hypotheses. The alteration process begins with the exfoliation of sheet edges. Then, from these lateral exfoliated sheets around the biotite monocrystal, an alteration front propagates along the sheets. The residual altered layer that develops is zoned, with an external zone composed of amorphous silica. This feature is in agreement with solution analyses, showing that Si is released at the slowest rate. This alteration layer acts as a diffusion barrier that controls the leaching of mobile cations (K, Mg, Fe, Al). This causes the leaching rates of all these elements to come under the control of silicon release in solution.

Alpha-Decay Damage of Cm-Doped Perovskite

AbstractCurium-doped perovskite slurry, which had the nominal composition of Ca0.98919(Cm, Pu)0.0108l Al0.0108l Ti0.98919O3, was calcined at 750°C for 2 h and then hot-pressed at 1250°C and 29MPa for 2 h. The hot-pressed cylinder samples had the specific 244Cm activity of 22.3 GBq·g−l on 31 March 1993. Their average density was 4.083 g·cm−3 after the samples got a cumulative dose of 0.7}1017 α decays·g−l. Change in density of Cm-doped perovskite reached 0.8% at a dose of 5}1017 α decays·g−l. The rate of density change was slightly larger in the present perovskite material than in Cm-doped Synroc reported previously. Half-disk perovskite specimens, which had accumulated doses of 1.6}1017 and 4.0}1017 α decays·g−l, were MCC-1 leach tested in pH˜2 solution at 90°C for two months. The leach rates of these specimens derived from weight losses were 1.7 and 2.3 g·m−2·day−l, respectively. These high leach rates caused a significant increase in pH in the later stage of the leaching runs. As-leached surfaces of Cm-doped perovskite showed the formation of anatase (TiO2). For the first 28 days, the Ca and Cm leach rates at the two different doses increased with leach time. More damaged specimens tended to give higher leach rates. In the final 28-day leaching run, both leach rates at the two different doses converged on each lower values although the Cm leach rate was lower than the Ca leach rate by a factor of &gt;20. Nonradioactive perovskite material showed similar changes in Ca leach rate and pH to the Cm-doped one although the as-leached surfaces of the former material showed much higher degree of alteration of perovskite to anatase.

Immobilization of stimulated high level wastes into AASC waste form

Alkali-activated slag cement (AASC) was studied as a host matrix for the immobilization of simulated high-level wastes. Experimental results show that, with a waste loading as high as 25%, AASC waste form presents high compressive strength (65–100 MPa), low porosity (less than 10%) and low leach rates (10 −5 and 10 −6 g/cm 2d for Cs and Sr, respectively). The mechanism of encapsulation of nuclides in AASC waste form was also studied.

Leaching of Al2O3-Based Nuclear Waste Forms.

Abstract The chemical durability of LaAlO3 and CaAl 12 O19 containing simulated high-level waste (HLW) elements (Nd, Ce and Sr) was examined at 90 and 150°C in HCl solution and deionized water. Because of the amphotericity of the major aluminium ions and the high solubility of the other matrix constituents, both waste forms dissolved congruently in HCl solution of pH 1 at 90°C, resulting in high leach rates of more than 10−3g. m−2.d−1 for all constituents. In deionized water, they dissolved incongruently, and leach rates of Al and Nd were less than 10−4g. m−2g.d−1. The leach rates in deionized water were lower than those of borosilicate glass waste forms by about 3 orders of magnitude. CaAl12O19 was superior to LaAlO3 in the durability in HCl solution and deionized water. It was found that the leach rates of Nd and Ce from both waste forms decreased with increasing temperature in deionized water. This phenomenon was attributed to the increase of pH resulting from the dissolution of Ca or Sr.