Leachable Phases Research Articles

Sodium carbonate roasting and mild acid leaching of vanadium titanomagnetite concentrates: Vanadium extraction and residue sodium decrease

Vanadium titanomagnetite is a crucial resource for vanadium and titanium. The traditional process of treating vanadium titanomagnetite concentrates has shortcomings like low vanadium recovery rate and titanium recovery inability, resulting in resource wasting and solid waste discharging. Thus, a new process of Na2CO3 roasting and mild H2SO4 leaching has been proposed. In the concentrates, titanium occurs majorly in titanomagnetite (Fe3-xTixO4, 0≤x≤1) and ilmenite (FeTiO3), vanadium in titanomagnetite and sphene (CaTiSiO5), calcium in sphene, and silicon and aluminum in several minerals. Phases are tuned during Na2CO3 roasting, where V and impurities Al and Si transform into soluble sodium compounds, leachable phase sphene doesn't change, and Ti is enriched in insoluble phases. Then, leached by mild H2SO4, the soluble compounds are almost all leached, and the leaching rates of V, Ca, Al, and Si are 91%, 76%, 84%, and 82%, respectively. The Na2O content in the leaching residue decreases to 1.0 wt%, which enables the residue for Ti extraction. This process is expected to recover V and Ti comprehensively from the vanadium titanomagnetite concentrates. The roasting kinetics are also studied based on CO2 content in the off-gas for a deeper understanding of the mechanism.

Comparative Study of Hydrogen Reduction of Bauxite Residue-Calcium Sintered and Self-Hardened Pellets Followed by Magnetic Separation for Iron Recovery

To minimize the carbon footprint in the industrial valourization of bauxite residue, hydrogen was used as a reducing agent. The current study experimentally investigated hydrogen reduction of bauxite residue-CaO sintered and self-hardened pellets at 1000 °C, along with magnetic separation of these reduced pellets for iron recovery. Calcium was introduced to bauxite residue to form leachable calcium aluminate phases with the existing alumina in bauxite residue. This involved the addition of either CaCO3 or a mixture of CaO and CaCO3 while maintaining the fixed Ca content during pelletization. The former underwent sintering at 1150 °C, while the latter was self-hardened through the cementing effect of CaO in exposure to moisture and air. Both types of pellets were reduced in a thermogravimetry furnace at an elevated temperature under similar conditions. The pellets were characterized by the X-ray diffraction (XRD) method and scanning electron microscope (SEM) coupled with energy dispersive spectroscopy (EDS), and their physical and mechanical properties were measured via standard techniques. During hydrogen reduction, a negligible amount of gehlenite (Ca2Al2SiO7) was formed in the self-hardened pellets, while this phase dominated in the sintered pellets. Alumina in the bauxite residue converted to mayenite phases during reduction in both the pellet types; however, reduced self-hardened pellets had a higher amount of alumina containing mayenite leachable phase. The two pellets showed similar reduction behaviour, while different chemical, physical, and mechanical properties were observed. The magnetic properties of milled reduced pellets were examined through a Davis Tube magnetic separator in a wet environment under a constant magnetic field of 800 G. Higher iron recovery was observed for the self-hardened reduced (41%) pellets than for the sintered pellets (27%).

Weathering stage and topographic control on rare earth element (REE) behavior: New constraints from a deeply weathered granite hill

Rare earth elements (REE) are sensitive tracers of rock-water interactions and soil formation processes. In this study, we investigated the REE concentration and distribution patterns for both bulk samples and acid leachable phase for a series of regolith and soil profiles developed on a deeply weathered granite hillslope in a subtropical climate. The exogenous input had little impact on the REE distributions on the studied hillslope. The REE distribution in the profiles was controlled by changes in the physical and chemical environmental parameters and mineral transformation during weathering. However, the specific mechanisms differed among the different weathering stages and profiles located at different positions along the slope. Among the environmental parameters, the profile redox state and acidity were the dominant factors controlling the REE behavior, with organic materials as the main regulators. A strong positive relationship between chemical index of alteration (CIA) and La/Yb was observed for the regolith samples, but the La/Yb ratio decreased upward from a depth of 120 cm (the bottom depth of the soil horizon) as the CIA value increased, suggesting a preference for light REE (LREE) fixation in kaolinite formed during the dissolution of feldspar; however, a conversion occurred during the subsequent pedogenesis period. The hilltop soil profile was characterized by the strongest LREE depletion and the highest positive Ce anomaly (~7.31–14.28), compared with other profiles down the hillslope (~0.84–2.78). The strongest LREE depletion on the hilltop profile JLN-S4 suggested a preference for LREE release resulting from the transformation of kaolinite to gibbsite, and the highest Ce anomaly indicates that Ce was fixed in a more oxidized environment within a well-drained profile. The hill foot profile JLN-S1 had the highest LREE leaching rate, but also the lowest heavy REE (HREE) leaching rate, which was ascribed to its lowest erosion rate, lowest pH value, and reductive conditions in a more hydromorphic zone down the hill. The releasing rates of REE calculated by a mass balance model at different positions along the catena ranged from 1395 to 14,379 μg m−2y−1. All the observed REE fractionation regimes and weathering rate variations along the hillslope illustrated that topography-regulated hydrologic condition played a critical role in the release and migration of REE during granite weathering.

Mineralogical Characterization and Acid Pretreatment of a Gold Calcine Leach Residue

Miners around Zimbabwe used to supply gold concentrates from sulphide flotation to the Kwekwe Roasting Plant (Zimbabwe) for toll treatment. The concentrates were roasted in Edward’s roasters and the calcine product was leached by cyanidation. Due to inefficient roasting, overall gold recoveries of 75–80% left behind a rich calcine leach residue at the Kwekwe Roasting Plant. The characterization performed to establish a potential process route involved several techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), fire assaying and inductively coupled plasma (ICP). Assays conducted on samples from the 350,000 tons tailings dam residue, created over the operational years, gave an average Au grade of 8.58 g/t and 12.54 g/t for Ag. The base metals assayed—0.11% Cu, 0.10% Pb, 0.17% Zn and 26.05% Fe. SiO2 (36.1%), Fe2O3 (36.9%), Mg3Si4O10 (OH)2 (8.9%), NaAlSi3O8 (6.9%), and Fe3O4 (6.4%)—were the major mineral phases in the cyanide leach residue. SEM gold scans on 24 polished sections showed only 2 discrete gold particles of less than 5 µm, with one partially liberated and associated with quartz, while the other was fully liberated. Therefore, the particulate gold in the calcine leach residue was negligible. It was deduced from the analysis after ultrafine milling (P80 < 5 µm) followed by cyanidation that 68.53% of the gold was sub-microscopic. Direct cyanidation using bottle roll resulted in only 2.33% of the total gold being leachable, indicating that the calcine leach residue was highly refractory. Diagnostic leaching by sequential use of acids in order of their strength resulted in HCl leachable phases (CaCO3, CaMg(CO3)2, PbS, Fe1-XS, and Fe2O3) freeing 4.2% of the total Au during subsequent cyanidation leach. H2SO4 leachable phases (Cu–Zn sulphides, labile FeS2) released an additional 26.57% during cyanidation, whereas HNO3 leachable phases (FeS2, FeAsS) released a further 20.98% of Au. After acid treatment and subsequent cyanidation, hot caustic leach of the residue followed by carbon in pulp resulted 4.43% of the total gold being eluted. Therefore, 4.43% of the total gold was surface bound. From the analysis after diagnostic acid leaching, it was deduced that a total of 54.08% of the gold was in the acid-leachable phase. Due to cost and environmental considerations, H2SO4 was selected for the evaluation of acid digestion as a pretreatment stage followed by cyanidation. Increasing the H2SO4 strength for the pretreatment of the calcine leach residue increased gold recoveries during cyanidation.

The Utilization of Bauxite Residue with a Calcite-Rich Bauxite Ore in the Pedersen Process for Iron and Alumina Extraction

Metallurgical grade alumina is produced worldwide through the well-known Bayer process, which unavoidably generates bauxite residue (BR, also known as red mud) in almost equal amounts to alumina. This study aims the valorization of BR through a smelting-reduction process to obtain calcium aluminate slags that can be a proper feed for alumina recovery via the Pedersen process. It investigates the thermodynamics and characteristics of the slags and pig iron produced from mixtures of BR, a bauxite beneficiation byproduct, and lime. In this context, the evolution of the different phases in the slags is studied with advanced analytical techniques and thermodynamic calculations. According to the results, a CaO/Al2O3 mass ratio within 1.3 to 1.4 in the slags can yield more Al2O3-containing leachable phases, such as CaO·Al2O3 and 12CaO·7Al2O3. The cooling dictates the amount and the characteristics of these phases, and the slower cooling rate yields improved slag characteristics. The distribution of the elements between the slag and metal phases shows that iron is separated, and the majority of the P, Cr, Ni, and V are distributed in the produced pig iron, while S, Ti, and Si are mostly concentrated in the slags.

Leaching kinetics and mechanism of slag produced from smelting-reduction of bauxite for alumina recovery

In the present study, we investigate the kinetics and mechanism of the leaching of calcium aluminate slag in Na2CO3 solution for alumina recovery. The slag consists of leachable phases, e.g., 12CaO·7Al2O3, CaO·Al2O3, 5CaO·3Al2O3, and a non-leachable phase that contains Ca-Al-Si-Ti oxides. A series of leaching treatment is done at different temperatures, leaching times, stirring rates, Na2CO3 concentrations, and different setups which includes wet-grinding and shaking-digestion reactor. The highest alumina recovery up to 90.5% is obtained after the slag is leached by 10 wt% Na2CO3 solution, at low temperatures (30–45 °C) within 90 min. It is shown that the rate of alumina recovery is high at the beginning of leaching and is then slow down due to the calcite layer product nucleation and growth at the surface of slag. The wet-grinding leaching and vigorous stirring increase the possibility of the collision between both particles and the stirrer that breaks the calcite layer, yielding less residue agglomeration and better recovery compared to the slow and mild agitations. A surface observation of the slag using electron microscopy shows that the calcite starts to nucleate at the non-leachable phase as the best deposition site, which has the least mass transfer barrier in the system. The apparent activation energy of the leaching reaction is calculated as 10.8–19.9 kJ/mol, which indicates the reaction is diffusion rate-limited as revealed by the applied kinetic models.

Comparison of structure, morphology, and leach characteristics of multi-phase ceramics produced via melt processing and hot isostatic pressing

Melt processing of multi-phase ceramic waste forms offers potential advantages over traditional solid-state synthesis methods given both the prevalence of melters currently in use and the ability to reduce the possibility of airborne radionuclide contamination. In this work, multi-phase ceramics with a targeted hollandite composition of Ba1.0Cs0.3Cr1.0Al0.3Fe1.0Ti5.7O16 were fabricated by melt processing at 1675 °C and hot isostatic pressing (HIP) at 1250 and 1300 °C. X-ray diffraction analysis (XRD) confirmed hollandite as the major phase in all specimens. Zirconolite/pyrochlore peaks and weaker perovskite reflections were observed after melt processing, while HIP samples displayed prominent perovskite peaks and low-intensity zirconolite reflections. Melt processing produced specimens with large (>50 μm) well-defined hollandite grains, while HIP yielded samples with a more fine-grained morphology. Elemental analysis showed “islands” rich in Cs and Ti across the surface of the 1300 °C HIP sample, suggesting partial melting and partitioning of Cs into multiple phases. Photoemission data revealed multiple Cs 3d spin-orbit pairs for the HIP samples, with the lower binding energy doublets likely corresponding to Cs located in more leachable phases. Among all specimens examined, the melt-processed sample exhibited the lowest fractional release rates for Rb and Cs. However, the retention of Sr and Mo was greater in the HIP specimens.

Chemical characterization of atmospheric dust from a weekly time series in the north Red Sea between 2006 and 2010

Atmospheric dust loads and chemical compositions serve as a key link between global climate patterns and marine biogeochemical cycles. The primary source of atmospheric dust in the world today is the Sahara-Arabian desert belt. Although this source was also active during the Quaternary, the interpretation of paleo-dust records and their effects on marine ecosystems is complicated by the scarcely reported atmospheric load patterns of bioavailable phases (i.e., water and acid leachable phases) and present-day contamination of anthropogenic components. This study reports a multi-annual time series of atmospheric dust loads (2006–2016) and their chemical compositions (2006–2010) collected in the north Gulf of Aqaba (north Red Sea) at a weekly to bi-weekly resolution. Major and trace element abundances in each sample are reported for three fractions: water-soluble salts, carbonates and oxides (weak acid leach), and Al-silicates.Dust loads vary seasonally from low values in late summer (∼20–30μgm−3) to higher values in the fall, and highest values in late winter and early spring (∼150–250μgm−3). Major and trace element abundances allow to distinguish between the sources and chemical compositions that dominate high and low dust loads in each season. The water leachable fraction (L0) is relatively enriched in Na, Ca, K and Mg, the acid-leachable fraction (L1) is enriched in Ca as well as Na, Al, Mg, Zn, Cd and Pb, and the silicate residue (L2) in Al and Fe.High dust loads occurring mainly during winter and spring months are characterized by low Mg/Ca (L1, L2), low K/Al and Na/Al (L1) and high Ca/Al (L1), high Mg/Al (L2) and relatively un-weathered (L2) contents. High dust load intervals during winter months are characterized by low passing air masses originating from the Sahara, while the ambient winter dust (low dust load) is associated with proximal source regions from the East Sahara and Arabian Peninsula. During late winter and spring months, high dust loads originate from central and west Sahara and to a lesser extent from north Sahara. Low dust loads characterize the summer with limited compositional variability relative to winter-spring months. Summer dust is generally characterized by high K/Al (L1) ratios relative to late winter and spring. It is also relatively high in anthropogenic trace elements in the L0 and L1 fractions (e.g., Zn/Al, Pb/Al, Cr/Al, Ni/Al and V/Al), whereby back trajectories indicate the source of these components is primarily from south and east Europe. The total load (ngm−3) of anthropogenic trace elements however, remains higher during winter and spring, stemming from the overall significantly higher dust loads characterizing this time window.The temporal load patterns of important micronutrients such as Fe, Cd, Zn, Cu, Ni and others in the bio-available phases (L0, L1) are not correlated with major nutrients or Chlorophyll-a sea surface concentrations, suggesting that the atmospheric dust plays a limited role in driving primary productivity in the oligotrophic surface waters of the Gulf of Aqaba.On a wider scale, the results provide unique chemical fingerprinting of Sahara-Arabian dust that can be applied to reconstruct past trends in dust loads recorded in deep-sea cores and other geological archives from this and other regions.

Leaching of Bornite Produced from the Sulfurization of Chalcopyrite

The pyrometallurgical route accounts for 80 pct of world metallic copper production, because chalcopyrite, the most abundant copper sulfide, is refractory to hydrometallurgical treatment. However, pyrometallurgical routes are quite restrictive as far as copper concentrates are concerned mainly owing to limits on the concentration of impurities, such as fluorine, chlorine, and arsenic that can be tolerated. Such concentrates require innovative processing solutions because their market value is greatly reduced. A potential alternative is the transformation of chalcopyrite to a sulfide amenable to leaching, such as chalcocite, covellite, or bornite, through treatment in either aqueous or gaseous environments. In this study, the sulfurization of a chalcopyrite concentrate containing 78 pct CuFeS2 in the presence of gaseous sulfur was investigated, with the goal of demonstrating its conversion to the leachable phases, i.e., bornite and covellite. The concentrate was reacted with elemental sulfur in a tubular furnace at temperatures ranging from 573 K to 723 K (300 °C to 450 °C), followed by atmospheric leaching in an Fe(III)-bearing solution. The mineral phases in the sample were quantified using the Rietveld method, and it was shown that at temperatures below 673 K (400 °C) chalcopyrite was converted to covellite (41 pct) and pyrite (34 pct), whereas at temperatures above these, the reaction products were bornite (45 pct) and pyrite (31 pct). Leaching tests [6 hours at 353 K (80 °C)] showed significantly higher copper extraction rates after sulfurization (90 pct) than those using the raw chalcopyrite concentrate (15 pct).

Melter Feed Reactions at T ≤ 700°C for Nuclear Waste Vitrification

To understand feed‐to‐glass conversion for the vitrification of nuclear waste, we investigated batch reactions and phase transitions in a simulated nuclear waste glass melter feed heated at 5 K/min up to 700°C using optical microscopy, scanning electron microscopy with energy‐dispersive X‐ray spectroscopy, and X‐ray diffraction. To determine the content and composition of leachable phases, we performed leaching tests; the leachates were analyzed by inductively coupled plasma atomic emission spectroscopy. By 400°C, gibbsite and sodium borates lost water and converted to amorphous phase, whereas other metallic hydroxides dehydrated to oxides. Between 400°C and 700°C, carbonates decomposed before 500°C; amorphous aluminum oxide and calcium oxide reacted with the sodium borate and formed the more durable amorphous borate phase along with intermediate crystalline products; above 500°C, quartz began to dissolve, and hematite started to convert to trevorite.

Biodisponibilidade de Metais-traço em Sedimentos: Uma Revisão

The chemical association of metal species in sediments provides indications about the release of trace metals by processes with toxic effects under certain environmental conditions. The knowledge of the way those metals are bond to sediments, serves to recognize specific sources of pollution in systems. Speciation plays an important role as far as bioavailability and toxicity are concerned. The accumulation of metal particles in sediments occur by the following mechanisms: a) Adsorption to the material fine particles (clay particles surface); b) precipitation of the element as carbonates, sulfates or oxides; c) co-precipitation of the element with iron and manganese oxides; d) complexation with the organic matter; e) incorporation into the crystal lattice of silicates. Currently, five phases are considered when studying the bioavailability of trace elements in sediments: a) exchangeable phase, MgCl 2 (causes change in salinity); b) leachable phase, acetic acid (causes pH change); c) reducible phase, hydroxylamine hydrochloride (allowing the release of metals in anoxic conditions); d ) oxidizable phase, hydrogen peroxide (causes the degradation of organic matter); e) pseudo-residual phase, aqua-regia (allows the release of metals associated with minerals). In the last two fractions, metals are strongly bound to the sediment constituents and are not available for animals and plants. The organic phase is relatively stable in nature and metals present therein are removed by strong oxidizing conditions. The metals contained in the pseudo-residual phase measure the degree of environmental pollution, since a large amount of metals present in this phase indicates a lower degree of pollution.

Elucidating the formation of terra fuscas using Sr–Nd–Pb isotopes and rare earth elements

Carbonate weathering mantles, like terra fusca, are common in Europe but their formation and evolution is still badly understood. We propose to combine geological, mineralogical and pedological knowledge with trace element and isotope data of a weathering mantle as a novel approach to understand the evolution of terra fuscas. Sr–Nd–Pb isotopes and rare earth element (REE) contents were analyzed in a cambisol developing on a typical terra fusca on top of a condensed Bajocian limestone-marl succession from the eastern side of the Paris Basin. The isotope data, REE distribution patterns and mass balance calculations suggest that the cambisol mirrors the trace element enrichments present in this carbonate lithology, which are exceptionally high compared to global average carbonate. The deeper soil horizons are strongly enriched not only in REE (ΣREE: 2640ppm) but also in redox-sensitive elements such as Fe (44wt.%), V (1000ppm), Cr (700ppm), Zn (550ppm), As (260ppm), Co (45ppm) and Cd (2.4ppm). The trace element distribution patterns of the carbonate bedrock are similar to those of the soil suggesting their close genetic relationships. Sr–Nd–Pb isotope data allow to identify four principal components in the soil: a silicate-rich pool close to the surface, a leachable REE enriched pool at the bottom of the soil profile, the limestone on which the weathering profile developed and an anthropogenic, atmosphere-derived component detected in the soil leachates of the uppermost soil horizon. The leachable phases are mainly secondary carbonate-bearing REE phases such as bastnaesite ((X) Ca(CO3)2F) (for X: Ce, La and Nd). The isotope data and trace element distribution patterns indicate that at least four geological and environmental events impacted the chemical and isotopical compositions of the soil system: 1. An oxygen-deficient diagenetic or hydrothermal event caused trace metal enrichments in the Bajocian limestone-marls. 2. Carbonate dissolution caused the enrichment of detrital silicate phases and authigenic REE-bearing residual phases – e.g. marine authigenic fluorapatites and bastnaesite – in the newly formed condensed horizons. 3. Dissolution/precipitation of metastable bastnaesite phases and downward migration of the REE during soil formation. 4. Overprinting of the chemical and isotopical compositions of the uppermost soil horizon by recent atmospheric depositions.

Evidence for intense REE scavenging at cold seeps from the Niger Delta margin

For many trace elements, continental margins are the location of intense exchange processes between sediment and seawater, which control their distribution in the water column, but have yet to be fully understood. In this study, we have investigated the impact of fluid seepage at cold seeps on the marine cycle of neodymium. We determined dissolved and total dissolvable (TD) concentrations for REE and well-established tracers of fluid seepage (CH 4, TDFe, TDMn), and Nd isotopic compositions in seawater samples collected above cold seeps and a reference site (i.e. away from any fluid venting area) from the Niger Delta margin. We also analyzed cold seep authigenic phases and various core-top sediment fractions (pore water, detrital component, easily leachable phases, uncleaned foraminifera) recovered near the hydrocast stations. Methane, TDFe and TDMn concentrations clearly indicate active fluid venting at the studied seeps, with plumes rising up to about 100 m above the seafloor. Depth profiles show pronounced REE enrichments in the non-filtered samples ( TD concentrations) within plumes, whereas filtered samples ( dissolved concentrations) exhibit slight REE depletion in plumes relative to the overlying water column and display typical seawater REE patterns. These results suggest that the net flux of REE emitted into seawater at cold seeps is controlled by the presence of particulate phases, most probably Fe–Mn oxyhydroxides associated to resuspended sediments. At the reference site, however, our data reveal significant enrichment for dissolved REE in bottom waters, that clearly relates to diffusive benthic fluxes from surface sediments. Neodymium isotopic ratios measured in the water column range from ε Nd ~−15.7 to − 10.4. Evidence that the ε Nd values for Antarctic Intermediate waters (AAIW) differed from those reported for the same water mass at open ocean settings shows that sediment/water interactions take place in the Gulf of Guinea. At each site, however, the bottom water ε Nd signature generally differs from that for cold seep minerals, easily leachable sediment phases, and detrital fractions from local sediments, ruling out the possibility that seepage of methane-rich fluids and sediment dissolution act as a substantial source of dissolved Nd to seawater in the Gulf of Guinea. Taken together, our data hence suggest that co-precipitation of Fe–Mn oxyhydroxide phases in sub-surface sediments leads to quantitative scavenging of dissolved REE at cold seeps, preventing their emission into bottom waters. Most probably, it is likely that diffusion from suboxic surface sediments dominates the exchange processes affecting the marine Nd cycle at the Niger Delta margin.

Effects of cement on redistribution of trace metals and dissolution of organics in sewage sludge and its inorganic waste-amended products

The suitability of using cement-stabilized sludge products as artificial soils in earth works was evaluated. The sludge products investigated were cemented sludge, cement-treated clay-amended sludge (SS + MC), and cement-treated copper slag-amended sludge (SS + CS). The leachability of lead (Pb), zinc (Zn), copper (Cu), and chromium (Cr) were assessed using the sequential extraction technique, toxicity characteristic leaching procedure (TCLP), NEN 7341 availability test, and column leaching test. The results indicated that Zn leachability was reduced in all the cement-stabilized sludge products. In contrast, Cu was transferred from the organic fraction to the readily leachable phases in the cement-stabilized sludge products and therefore exhibited increased leachability. The increased Cu leachability could be attributed to dissolution of humic substances in the sludge as a result of elevated pH. Good correlation between dissolved organic carbon (DOC) and heavy metal leaching from the cement-stabilized sludge products was observed in the column leaching experiment. Even with a cement percentage as small as 12.5%, calcium silicate hydrate (C–S–H) was formed in the SS + MC and SS + CS products. Inclusion of the marine clay in the SS + MC products could reduce the leaching potentials of Zn, and this was the great advantage of the marine clay over the copper slag for sludge amendment.

Beryllium geochemistry constraints on the hydraulic behavior of mud volcanoes: the Trinidad Island case

To constrain Trinidad mud volcanoes hydraulic behavior, both cosmogenic 10Be (t1/2=1.5 Myr) and 9Be concentrations have been measured in fluid and associated expelled mud. As previously evidenced [A.N. Dia, M. Castrec, J. Boulègue, P. Comeau, Trinidad Mud Volcanoes: where do the expelled fluids come from? Geochim. Cosmochim. Acta 63 (1999) 1023–1038] from δ18O values and Cl concentrations, 9Be concentrations in the fluids mostly reflect the mixing of two deep components: REM I and REM II. REM I (δ18O=10.5‰, Cl≈275 mM and 9Be≈0.05 nM) has characteristics of a continental fluid while REM II (δ18O=3‰, Cl≈350 mM and 9Be≈1 nM) results from seawater–volcanogenic derived sediment interaction. Although 10Be concentrations in the fluid samples are close to the detection limit, the distribution of both beryllium isotopes between the hydroxylamine leachable and residual phases indicates exchange reaction with fluid younger than 15 Myr. Comparison between the lowest REM I 10Be/9Be ratio in fluid recorded by the hydroxylamine leachable phase (TD5 mud sample) and the 10Be/9Be ratio representative of meteoric contribution in the recharge area (TD8 fluid sample) yields a circulation rate of REM I fluid in the Trinidad mud volcanoes of several 10−1 m/yr.

Host phase of239,240Pu and241Am in deep-sea sediment

Host phases of fallout239,240Pu and241Am were studied in the surface sediments obtained in 1994 from abyssal basins of relatively small area of the western North Pacific. An analytical procedure involving sequential chemical extraction was employed for partitioning the host phases of the nuclides in sediment into five fractions: (1) exchangeable (2) bound to carbonate, (3) bound to hydrous Fe-Mn oxides, (4) bound to organic matter and (5) residual. Decrease of total239,240Pu concentration with decreasing association of239,240Pu with organic matter, high241Am/239,240Pu activity ratio in carbonate phase and somewhat high proportion of oxidized239,240Pu in leachable phases suggest a possibility of post-depositional diagenetic remobilization of Pu from sediment to water column.

98/04218 Long-term experience with non-catalytic nitrogen oxide removal in coal-fired boilers in the Czech Republic

The suitability of using cement-stabilized sludge products as artificial soils in earth works was evaluated. The sludge products investigated were cemented sludge, cement-treated clay-amended sludge (SS + MC), and cement-treated copper slag-amended sludge (SS + CS). The leachability of lead (Pb), zinc (Zn), copper (Cu), and chromium (Cr) were assessed using the sequential extraction technique, toxicity characteristic leaching procedure (TCLP), NEN 7341 availability test, and column leaching test. The results indicated that Zn leachability was reduced in all the cement-stabilized sludge products. In contrast, Cu was transferred from the organic fraction to the readily leachable phases in the cement-stabilized sludge products and therefore exhibited increased leachability. The increased Cu leachability could be attributed to dissolution of humic substances in the sludge as a result of elevated pH. Good correlation between dissolved organic carbon (DOC) and heavy metal leaching from the cement-stabilized sludge products was observed in the column leaching experiment. Even with a cement percentage as small as 12.5%, calcium silicate hydrate (C–S–H) was formed in the SS + MC and SS + CS products. Inclusion of the marine clay in the SS + MC products could reduce the leaching potentials of Zn, and this was the great advantage of the marine clay over the copper slag for sludge amendment.

Os isotopic systematics of the MORB mantle: results from altered abyssal peridotites

Abyssal peridotites are fragments of the oceanic upper mantle. Previous studies have indicated that their Os isotopic compositions span a wide range, including values more radiogenic than most estimates of the average bulk Earth 187 Os 188 Os ratio. This is difficult to reconcile with their derivation as residues of MORB partial melting. We present results that suggest that some of this variation, particularly the higher values, may be of secondary origin. Comparison of altered rims and unaltered cores of two mylonitic peridotites reveal that submarine weathering can increase 187 Os 188 Os ratios by more than 5%. Leaching experiments demonstrate the presence of a radiogenic, easily leachable phase that is most easily explained as a seawater-derived component. Thus, Os isotopic results from abyssal peridotites must be interpreted with some caution unless it can be shown that the effects of seawater alteration were minor. We develop criteria based on Sr and Nd isotopic measurements, as well as major element compositional changes, that allow strongly altered samples to be identified. Applying these criteria, we find 10 samples, including literature data as well as new analyses, that have apparently suffered only minimal alteration. These samples range in 187 Os 188 Os from 0.1221 to 0.1270, with a mean of 0.1246 and a standard deviation of 0.0014. Thus, we see no evidence for depleted mantle rocks more enriched in 187 Os 188 Os than the preferred value of ∼ 0.127. Finally, if Os is lost from peridotites during weathering, it may provide a significant source of mantle Os to the world's oceans.

The influence of temperature and NaCl on cadmium, copper and zinc partitioning among suspended particulate and dissolved phases in an urban river

Distribution coefficients ( K d) were used to estimate the most important geochemical phases within the suspended particulate matter (SPM) pool for sorption of Cd, Cu and Zn. Given that pH effects were expected to be minimal, as the don is a well buffered system, the possible influence of secondary environmental variables [temperature, dissolved organic carbon (DOC), dissolved Ca 2+ and NaC] on trace metal partitioning between SPM and the dissolved phase was evaluated using a series of multiple linear regressions for total ( K d T) as well as the phase specific K d L leachable phase; K d R reducible phase; and K d O oxidizable phase) distribution coefficient estimates. The three metals varied in their sorptions patterns. Cd and Zn showed the same relative affinities for three SPM pools (leachable = reducible > oxidizable), while Cu affinities ranked oxidizable = leachable > reducible. Secondary environmental factors were identified as more important influences on trace metal partitioning than pH. Temperature and NaCl (from road salt runoff) were found to be key environmental variables influencing trace metal partitioning. A decrease in water temperature caused decreases in the accumulation of Cd, Cu and Zn in the particulate pool. Increasing NaCl concentrations decreased the concentrations of Cd and Zn associated with the particulate leachable phase and the Cd, Zn and Cu content in the oxidizable SPM phase. These results suggest that in running waters during winter months, or even during summer months in the hypolimnia of sufficiently deep lakes, a relatively higher proportion of these metals remains in the dissolved and potentially more bioavailable pool.

Beryllium isotope geochemistry of hydrothermally altered sediments

Profiles of both 10Be and 9Be concentrations have been measured in sediments from the DSDP, Leg 64, Site 477 core. Established in the deep Guaymas Basin, in an area of high heat flow, this site offers the opportunity of studying hydrothermal alteration induced by two distinct hydrothermal systems, those caused (i) by the intrusion of hot sills into porous sediments and (ii) by heat associated with a magma chamber. The results show that the distribution of both beryllium isotopes between two operationally defined sedimentary phases (material susceptible to hydroxylamine leaching and residual material) changes with the degree of hydrothermal alteration. A decrease in 10Be/ 9Be in the leachable phase of altered sediments relative to unaltered sediments indicates that hydrothermal alteration is not limited to a simple chemical leaching but involves redistribution of the beryllium isotopes between metamorphosed sedimentary phases. In addition, the similarity of the mean 10Be/ 9Be ratios associated with the leachable and the residual phases in the part of the core which has experienced greenschist facies metamorphism suggests that this process leads in the prevailing geophysical conditions to isotopic homogenization. A close relationship exists between 10Be and MgO concentrations in altered sediments from this core. This supports earlier observations that beryllium is not easily removed from the sedimentary column and indicates that this remains the case even under the conditions encountered in submarine hydrothermal systems.