Melting Of Base Metal Research Articles

Metal contamination in alkaline Phantom Lake (Flin Flon, Manitoba, Canada) generates strong responses in multiple paleolimnological proxies

The copper-zinc smelter at Flin Flon (Manitoba) operated between 1930 and 2010 and emitted large amounts of metal(loid)s and sulphur dioxide into the atmosphere, damaging the surrounding terrestrial landscapes and depositing airborne industrial pollutants into aquatic ecosystems. However, the extent of biological impairment in regional lakes is largely unknown. Here, we analysed biological and geochemical proxies preserved in a dated sediment core from Phantom Lake, collected seven years after the smelter closed in 2010. Our objectives were to determine how smelting history affected long-term trends in (1) sedimentary elements, (2) biota across multiple trophic levels, and (3) spectrally-inferred chlorophyll a and lake-water total organic carbon. The effects of smelting activities were clearest in the diatom record, in concordance with modest responses in chironomid and cladoceran assemblages. Several metal(loid)s were naturally high and exceeded sediment quality guidelines during the pre-smelting era. With the opening of the smelter, metal(loid) concentrations in sediments increased through the 1930s, peaked in the 1960s, and declined thereafter with technological improvements but remained above background to this day. Although modest declines in inferred lake-water total organic carbon indicate reduced terrestrial carbon supply following sulphate deposition in the catchment, the diatom record showed no evidence of acidification as the lake was and remained well-buffered. Pre-smelting diatom and invertebrate assemblages were diverse and indicated oligo-mesotrophic conditions. Smelting was associated with the loss of metal-sensitive biological indicators and the emergence of assemblages dominated by metal-tolerant, generalist taxa. Diatoms tracked substantial reductions in aerial emissions since the 1990s, particularly after the smelter closed, but also indicated that the biological effects of metal pollution persist in Phantom Lake. Examining the effects of a base metal smelter on a well-buffered lake offered insights into multi-trophic level responses to severe metal contamination and potential recovery without the confounding effects of concurrent changes in lake acidity.

The Ceramic Composite Coating (TiC+TiB2) by ESD on Ti6AL4V Alloy and Its Characterization

Titanium based alloys or materials used for mechanical and constructional purposes can exhibit high corrosion and abrasion resistance with coatings made on their surfaces. In this study, the surface of Ti6Al4V plate substrate was coated with TiC+TiB2 composite electrodes at different volts and frequencies by Electro-Spark Deposition (ESD) method. The ESD method is a micro arc welding method that allows deposits of alloys and ceramics compounds that have electrical conductivity on the surface of metallic materials, with the plasma that brings about a better melting of base metal and electrode for producing good adhesion between the coating and base metal. In this study, the Ti6Al4V samples were coated with TiC+TiB2 electrodes, and the precoating, post-coating hardnesses, wear rates and coating layer thicknesses of the samples were examined. TiC + TiB2 composite coating on the surface of Ti6Al4V alloys by ESD method was achieved and the hardness increase was observed with the help of numerous hard ceramic phases.

Influence of Novel Torch Type on Mechanical and Microstructural Characteristics of Cold Metal Transfer Brazed Joints

Abstract The present study aimed to braze interstitial free (IF) steel by using novel Braze+ and conventional Robacta torches with the aid of CuAl8 filler wire for a range of heat input 72–250 J/mm. Results showed that focused/denser arc and smaller arc action range, i.e., lower heat loss in the case of Braze+ torch resulted in better wettability, thicker intermetallic layer at the interface of deposited bead-steel, and higher dispersive phase fraction in the bead compared to Robacta torch which ultimately contributed to the evolution of mechanical properties of brazed joints. Furthermore, wettability, thickness of intermetallic layer and fraction of dispersive phases increased with the heat input due to increased deposition rate per unit time, availability of reacting atoms near the interface, and melting of base metal, respectively. Hardness variation of the brazed joints revealed that base metal was prone to failure due to comparatively higher hardness as well as improved resistance to failure of HAZ (due to the formation of acicular ferrite) and deposited bead (due to dispersion hardening). In addition, Fe, Al, and Cu were the main constituents of intermetallic layer and dispersive phases in the bead. IMC layer was harder in the case of Braze+ torch due to comparatively higher Fe content. Two modes of failure namely interface (brittle features) and base metal (ductile features) were observed during shear-tensile testing.

Adjust dilution level to suppress the precipitated phase by dilution level model of dissimilar metal laser welding with filler wire

To suppress the precipitated phase by adjusting the dilution level of 304 in the dissimilar metal (Hastelloy C-276/SUS 304) laser welding with filler wire, a mathematical model was established between laser parameters and the dilution level of 304 through energy conservation and mass conservation. And the model was verified by the corresponding experiment. The dilution level of 304 is linear with the single pulse energy E and inverse of wire feeding speed (1/VF), and it is also affected by energy melting efficiency and the ratio of two base metals melting. The dilution level of 304 is positively correlated with energy melting efficiency and negatively correlated with the ratio of two base metals melting. Defocusing distance and pulse width can affect dilution level of 304 by changing energy melting efficiency. Welding speed and laser beam offset can affect dilution level of 304 by changing the ratio of two base metals melting. At the same time, the influencing mechanism of the dilution level of 304 on the precipitated phase is revealed. The precipitated phase is directly related to the dilution level of 304. With the increase of dilution level of 304, the volume fraction of precipitated phase increases first and then decreases. When the dilution level of 304 is 24.0% ~ 35.2%, the volume fraction of precipitated phase is the biggest. And when the dilution level of 304 arrives to about 73.0%, the precipitated phase approximately disappears. As the result, the dilution level of 304 can be adjusted to suppress the precipitated phase by the dilution model in the laser welding Hastelloy C-276/SUS 304 with filler wire.

Dissimilar Metal Joining of 304 Stainless Steel to SMA490BW Steel Using the Filler Metal Powders with a High-Entropy Design

High-entropy alloys having excellent properties are particularly suitable for the application as the filler metals in welding. In the present study, multi-component mixed powders of FeCoCrNiMn and CrFeNi2.4Al0.6, based on a high-entropy design, as well as the comparative 316L stainless steel powders, were used as the filler metals, to achieve the dissimilar welding between 304 stainless steel and SMA490BW steel by laser deposition welding. By comparative analysis of the microstructure and mechanical properties of three types of joints, the feasibility and weld-ability of the filler metal powders based on a high-entropy design were studied. It was found that the melting of base metal (BM) and weld metal dilution had an impact on the set high-entropy component in the weld zone. And high-entropy structures were achieved in the weld zone by using the powders of CrFeNi2.4Al0.6. Compared to the BM of SMA490BW steel, three types of joints presented a higher notched tensile strength and had a better corrosion resistance. The joint welded using the powders of CrFeNi2.4Al0.6 had the lowest hardness value in the weld zone, in which the joint was fractured during the notched tensile tests. The other two joints fractured near the notch in the SMA490BW steel side. Transgranular fracture and a typical dimple fracture were observed in the fractured joints. In this work, multi-component mixed powders of FeCoCrNiMn and CrFeNi2.4Al0.6, based on a high-entropy design, were used as the filler metals to achieve the dissimilar welding of 304 stainless steel to SMA490BW steel by laser deposition welding. And a detailed investigation of microstructures and mechanical properties of those dissimilar joints was carried out to explore the feasibility and weld-ability of the filler metal powders based on a high-entropy design.

Development of hybrid welding processes incorporating GMAW and SMAW

Abstract Present work aims to increase the weld strength by combining Metal Inert Gas Welding (MIG) and Shielded Metal Arc Welding and reduce the dependence on inert gas used in MIG welding by relying on the flux of electrode to provide the shielding effect. It also aims to reduce the HAZ by reducing the melting of base metal, instead filling the grooves by molten mild steel electrode which is used in SMAW. Steel plates (IS-2062 grade) of 6mm thickness were welded in a single pass by placing a mild steel electrode (E6013) between them. The Shielding Gas used was CO2. Pre-weld preparations included making grooves with various included angles and Root gaps. Characterization was done using Optical Microscope. Micro-hardness test was carried out to confirm the above results. As flux of the electrode forms shielding gas and slag on the top of the weld, flow rate of the gas can be reduced to a much lower extent.

Active-Controlled Passive Distribution of Power Offers Efficient Heat Treating Solution for Quality Arc Welding Joints of Steel Pipes

Using high energy density welding arc, the joining process makes pipe joints involving melting of base metal. The thermal cycle could cause distortion and have residual stress around joints and there could be a prospect of hydrogen cracking. By employing proper heat treatment procedures, the physical, metallurgical, and mechanical properties of steel structures are regained for their long endurance under extreme operating conditions of pressure and temperature, particularly, in power industries. The joints need to undergo pre- and post-weld heat treatment. Induction heating is increasingly being used for heat treatment of pipes, tubes, pressure vessels, etc., made up of a special type of steel such as P91 Grade. As the popularity of the heat treatment process is on the rise, it is important to look into the energy efficiency and power delivery aspects of the system. This paper proposes an innovative method to configure the induction heating controller and the tank circuit so that the energy delivery to the pipe and its usage are inherently improved. The proposed ideas have been practically demonstrated using a 40–45 kW induction heater.

Nanomineralogy as a new dimension in understanding elusive geochemical processes in soils: The case of low-solubility-index elements

Abstract Nanomineralogical studies of mineral surface coatings in soils reveal insights into biogeochemical processes that heretofore were not known to exist. This is a new dimension in understanding past and present biogeochemical processes in soils, and in this study it is a way to better understand the behavior of low-solubility-index elements such as Al, Ti, and Zr. Soils were sampled from selected sites in Sudbury (Ontario, Canada) that have been affected by acidification and particulate matter emissions from base-metal smelters with subsequent remediation within the past century. These anthropogenic processes have affected an entire landscape, but are now recorded in assemblages of nano-size phases that can be only studied using a combination of focused ion beam technology (for sample preparation) and high-resolution analytical transmission electron microscopy (for phase identification). A first generation of clay minerals (pre-acidification phase), their partial replacement by nano-size hematite and amorphous silica (anthropogenic acidification), and a second generation of clay minerals (post-acidification, including soil remediation) are products of changes in soil biogeochemical processes during these natural and anthropogenic-induced weathering stages. Complex assemblages of nanophases formed prior to the second generation of clay minerals depict underlying mechanisms for the mobilization and sequestration of the low-solubility-index elements Zr and Ti under acidic conditions. The occurrence of baddeleyite (ZrO2), anatase (TiO2), and the Magneli phases Ti4O7 and Ti5O9 (all present at the nanoscale) suggest an influx of nanocolloidal Zr and Ti oxides during weathering of smelter-derived particulate matter. Kelyshite {NaZr[Si2O6(OH)]}, authigenic zircon (ZrSiO4), and kleberite [Fe3+Ti6O11(OH)5] are most likely products of the sequestration of the Zr- and Ti-bearing nanocolloids.

Optically controlled local nanosoldering of metal nanowires

Nanojoining (including nanowelding, nanosoldering, etc.) of metal nanomaterials offers the opportunity of constructing complex structures and advanced functional devices at the nanoscale. In comparison with nanowelding, nanosoldering does not involve the melting of base metal and shows considerable mechanical strength and good thermal and electrical conductivity. Here, an optically controlled local nanosoldering technique, which ensures the nanostructures to be bonded while their original structural integrity is retained, is proposed and demonstrated. Typical elemental devices (V-shaped, T-shaped, and X-shaped nanostructures) are formed with this nanosoldering technique. The conductivity of one V-shaped junction is enhanced by 500 times after nanosoldering. This facile nanosoldering technique provides an avenue to locally manipulate light, charge, heat, and mass transport at the nanoscale and is thereby expected to benefit the development of nanophotonics and nanoelectronics.

Detection and Mapping of Black Rock Coatings Using Hyperion Images: Sudbury, Ontario, Canada

Base metal smelting activities can produce acidic rain that promotes vegetation loss and the development of black coatings on bedrock. Such coatings can form over large areas and are among the most prominent long-term vestiges of past smelting activities. In this study, multispectral images derived from Hyperion reflectance data were evaluated with regard to their utility in the discrimination and mapping of black rock coatings near Sudbury. Spectral angle mapper (SAM) classifications generated on the basis of image-derived endmember spectra could not be used to properly identify major exposures of coated bedrock without also producing substantial confusion with uncoated classes. Neural network and maximum likelihood classifications produced improved representations of the spatial distribution of coated bedrock, though confusion between coated and uncoated classes is problematic in most outputs. Maximum likelihood results generated using a null class are noteworthy for their effectiveness in highlighting exposures of coated bedrock without substantial confusion with uncoated classes. Although challenges remain, classification results confirm the potential of remote sensing techniques for use in the worldwide detection, mapping, and monitoring of coating-related environmental degradation in the vicinities of base metal smelters.

Major correlates of mercury in small fish and common loons (Gavia immer) across four large study areas in Canada

We investigated mercury (Hg) concentrations in small fish (mainly yellow perch, Perca flavescens; ∼60% of fish collected) and in blood of common loons (Gavia immer) that prey upon them during the breeding season on lakes in 4 large, widely separated study areas in Canada (>13 lakes per study area; total number of lakes = 93). Although surface sediments from lakes near a base metal smelter in Flin Flon, Manitoba had the highest Hg concentrations, perch and other small fish and blood of common loon chicks sampled from these same lakes had low Hg concentrations similar to those from uncontaminated reference lakes. Multiple regression modeling with AIC analysis indicated that lake pH was by far the most important single factor influencing perch Hg concentrations in lakes across the four study areas (R2 = 0.29). The best model was a three-variable model (pH + alkalinity + sediment Se; Wi = 0.61, R2 = 0.85). A single-variable model (fish Hg) best explained among-lake variability in loon chick blood Hg (Wi = 0.17; R2 = 0.53). From a toxicological risk perspective, all lakes posing a potential Hg health risk for perch and possibly other small pelagic fish species (where mean fish muscle Hg concentrations exceeded 2.4 μg/g dry wt.), and for breeding common loons (where mean fish muscle Hg concentrations exceeded 0.8 μg/g dry wt., and loon chick blood Hg exceeded 1.4 μg/g dry wt.) had pH < 6.7 and were located in eastern Canada.

Visualisation and quantification of heavy metal accessibility in smelter slags: The influence of morphology on availability

The Imperial Smelting Furnace (ISF) for producing lead and zinc simultaneously has operated on four continents and in eleven countries from the 1950's. One of the process changes that the ISF introduced was the production of a finely granulated slag waste. Although this slag contained significant amounts of residual lead (Pb) and zinc (Zn), because of its glassy nature it was considered environmentally benign. From the Cockle Creek smelter near Boolaroo at the northern end of Lake Macquarie, NSW, Australia, it is estimated that around 2.1 million tonnes of the fine slag was distributed into the community and most remains where it was originally utilised. Residual tonnages of slag of this magnitude are common worldwide wherever the ISF operated. Studies of base metal smelting slags have concluded that mineralogical and morphological characteristics of the slag play a critical role in moderating environmental release of toxic elements. Scanning electron microscopy (SEM) and microanalysis of the ISF slags has shown that the Pb and associated elements are present as discrete nodules (∼6–22 μm) in the slag and that they are not associated with Zn which is contained in the glass slag phase. Using an automated SEM and analysis technique (QEMSCAN®) to “map” the mineralogical structure of the particles, it was possible to quantitatively determine the degree of access infiltrating fluids might have to the reaction surface of the Pb phases. The level of access decreases with increasing particle size, but in even the largest sized particles (−3350 + 2000 μm) nearly 80% of the Pb-containing phases were totally or partially accessible. These results provide evidence that the toxic elements in the slags are not contained by the glassy phase and will be vulnerable to leaching over time depending on their individual phase reactivity.

Soil-Air Mercury Flux near a Large Industrial Emission Source before and after Closure (Flin Flon, Manitoba, Canada).

Prior to its closure, the base-metal smelter in Flin Flon, Manitoba, Canada was one of the North America's largest mercury (Hg) emission sources. Our project objective was to understand the exchange of Hg between the soil and the air before and after the smelter closure. Field and laboratory Hg flux measurements were conducted to identify the controlling variables and used for spatial and temporal scaling. Study results showed that deposition from the smelter resulted in the surrounding soil being enriched in Hg (up to 99 μg g(-1)) as well as other metals. During the period of smelter operation, air concentrations were elevated (30 ± 19 ng m(-3)), and the soil was a net Hg sink (daily flux: -3.8 ng m(-2) h(-1)). Following the smelter closure, air Hg(0) concentrations were reduced, and the soils had large emissions (daily flux: 108 ng m(-2) h(-1)). The annual scaling of soil Hg emissions following the smelter closure indicated that the landscape impacted by smelter deposition emitted or re-emitted almost 100 kg per year. Elevated soil Hg concentrations and emissions are predicted to continue for hundreds of years before background concentrations are re-established. Overall, the results indicate that legacy Hg deposition will continue to cycle in the environment long after point-source reductions.

A Landsat-based study of black rock coatings proximal to base metal smelters, Sudbury, Ontario, Canada

Past emission of metal-bearing particulate matter, sulphur dioxide (SO2), and sulphuric acid by base metal smelters in the Sudbury region led to widespread loss of vegetation, contamination of soils, and formation of black coatings on rock surfaces. These black coatings formed through the incorporation of smelter-borne particulate matter into the partly dissolved uppermost layers of siliceous minerals on exposed rock, and are characterized by high heavy-metal content. This study involved assessment of the reflectance properties of black coatings in the Sudbury region, and determination of the geographic distribution of coatings through supervised classification of reflectance data derived from a Landsat Enhanced Thematic Mapper Plus (ETM+) image. Classifications involved the use of the Spectral Angle Mapper (SAM), Maximum Likelihood, and Feedforward Backpropagation Neural Network algorithms. The reflectance spectra of black coatings in the Sudbury region are relatively flat and featureless, and are characterized by reflectance values less than ~13% across the visible, near-infrared, and short-wave infrared. Spectral properties are similar to those of magnetite, a spinel-group mineral known to be present in Sudbury coatings. The presence of carbon-rich soot particles may be an important influence on the reflectance properties of coatings. SAM classification results are characterized by the widespread mislabelling of uncoated urban and open-pit sites as mantled by black coatings, and neural network results problematically mislabel some uncoated wetland sites as coated. Results generated by the Maximum Likelihood algorithm most usefully depict the distribution of exposed black coatings in the Sudbury region. The mapping of black coatings using remote-sensing methods can provide useful information on the spatial character of environmental degradation in the vicinity of smelters, and should be helpful in the monitoring of environmental recovery where emissions have been reduced or eliminated.

Extensive weathering of zinc smelting slag in a heap in Upper Silesia (Poland): Potential environmental risks posed by mechanical disturbance of slag deposits

Slags from base metal smelting are often deposited for over 100years with no barriers between the heap and the surrounding environment. Observations at the external surfaces of the slag heaps may not reflect the state of the slag material inside the slag heap. A slag heap from Zn–Pb ore smelting (Świętochłowice, Upper Silesia, Poland) was disturbed during recent slag removal and the freshly uncovered surfaces are examined in this study. The material forming the interior of the slag heap is fine-grained (up to 5cm) and strongly weathered (called the weathered slag zone) in contrast to the large slag boulders on the surface of the slag heap (up to 2m), which are only slightly weathered. The weathered slag zone is composed of gypsum and hematite plus a mixture of primary and other secondary phases. The weathered material as a whole is chemically more homogenous than unweathered slags and has lower Si and higher Fe, Pb (up to 3wt.%) and Cd (up to 560mg/kg) concentrations. SEM images show that primary slag phases are porous and disintegrated. The examined surfaces are 3–4m high and 10–30m wide suggesting that such slag weathering may have occurred in more extensive parts of the slag heap. Weathering affects slag types with different phase compositions and is therefore controlled by specific conditions occurring within the heap, not by the type of slag. These conditions are so far not well defined, but may include prolonged slag deposition, slow water transfer within the heap and interaction of slags with acid rains common in the Upper Silesia region.The weathered slag zone, when confined within the slag heap, acts as a sink for many potentially toxic elements, decreasing their release to the environment. However, this may change dramatically when the zone is uncovered and its deposit conditions change. Potential risks encompass release of potentially toxic elements from the heap, transport of fine grained particles to the surrounding environment and release of elements when the material is deposited in nearby soils or waters, as well as when it is reused as a construction material.

Effect of Friction Stir Welding on Microstructural and Mechanical Properties of Copper Alloy

Abstract —This study demonstrates the feasibility of joining the commercial pure copper plates by friction stir welding (FSW). Microstructure, microhardness and tensile properties in terms of the joint efficiency were found 94.03 % compare to as receive base material (BM). The average hardness at the top was higher than bottom. Hardness of weld zone was higher than the base material. Different microstructure zones were revealed by optical microscopy and scanning electron microscopy. The stirred zone (SZ) exhibited primary two phases namely, recrystallized grains and fine precipitates in matrix of copper. Keywords —Welding; FSW; Commercial Copper; Mechanical properties I. I NTRODUCTION RICTION stir welding (FSW) is a new solid state welding process, where the weld is produced by softening, plastic deformation combined with forging action caused by tool rotation of base metal (Fig. 1) [1-3]. Absence of melting of base metal in FSW reduces oxidation, residual stress, solidification related defects. The microstructure of the weld generally shows a central weld nugget with onion ring structure, a thermo-mechanically affected zone (TMAZ) close to the nugget, and a very small heat affected zone (HAZ) [4]. Recently many reports on friction stir welding of various metal system such as aluminium [5-10], magnesium [11-12], mild steel [13], stainless steel [14], and dissimilar systems such as aluminium to stainless steel [15], aluminium to steel [16], aluminium to copper [17], aluminium to magnesium [18], have been published. Preliminary studies on the FSW for copper to copper [19-21] and brass [22-23] have also been reported. Copper and its alloys are widely used in industrial applications due to their excellent electrical and thermal conductivities, good strength, and corrosion and fatigue resistances.

A new method for the characterisation and quantitative speciation of base metal smelter stack particulates

Base metal smelters may be a source of particulates containing metals of environmental concern released to the atmosphere. Knowledge of the quantitative chemical speciation of particulate releases from base metal smelters will be of value in smelter emission fingerprinting, site-specific risk assessments, predictions of the behaviour of smelter stack particulates released to the environment and in resolving liability issues related to current and historic releases. Accordingly, we have developed an innovative approach comprising bulk chemical analysis, a leaching procedure, X-ray diffraction analysis and scanning electron microscopy/electron probe microanalysis characterisation in a step-wise apportioning procedure to derive the quantitative speciation of particulate samples from the stacks of three copper smelters designated as A, B and C. For the A smelter stack particulates, the major calculated percentages were 29 CuSO(4), 20 ZnSO(4).H(2)O, 13 (Cu(0.94)Zn(0.06))(2)(AsO(4))(OH), 11 PbSO(4) and four As(2)O(3). For the B smelter stack particulates, the primary calculated percentages were 20 ZnSO(4).H(2)O, 20 PbSO(4), 12 CuSO(4) and nine As(2)O(3). Finally, we calculated that the C smelter stack particulates mostly comprised 34 ZnSO(4).H(2)O, 19 (Cu(0.84)Zn(0.16))(AsO(3)OH), 11 PbSO(4), 10 As(2)O(3) and nine Zn(3)(AsO(4))(2). Between 56% and 67% by weight of the smelter stack particulates, including the As, was soluble in water. For these and other operations, the data and approach may be useful in estimating metals partitioning among water, soil and sediment, as well as predictions of the effects of the stack particulates released to the environment.

Effect of annealing treatment on the crystallisation and leaching of dumped base metal smelter slags

Leaching tests of base metals contained in two smelter slags were undertaken in ammonia and nitric acid solutions aiming to recover Co, Cu and Zn. Leaching tests were conducted at 25 and 60 °C at pH = 0 and 3 in HNO 3 and pH = 12 in NH 4OH media. XRD analysis revealed that the dumped slags were amorphous. Annealing these slags at 1180 °C produced crystalline phases comprising diopside, magnetite and fayalite. SEM and EDS analysis revealed that Cu and Pb compounds have concentrated in the magnetite phase, whereas another phase rich in Zn and Cu was located in the diopside matrix. ICP-OES analysis of the pregnant leaching solutions (PLS) showed that 30–60% of Co, Cu and Zn were released from the amorphous slags treated in HNO 3 at pH = 0, and lesser in ammonia. However, the contamination by Fe and Pb was higher at pH = 0. The contamination of the PLS obtained by leaching of the crystallised slags remained low. The low Fe and Pb contamination was attributed in this case to the chemical stability of the crystalline phases formed upon annealing treatment. The higher solubilisation of metals contained in amorphous slags was attributed to the collapse of silicate structures during nitric acid leaching at pH ∼ 0.

Cadmium, lead and zinc leaching from smelter fly ash in simple organic acids—Simulators of rhizospheric soil solutions

Emissions from base-metal smelters are responsible for high contamination of the surrounding soils. Fly ash from a secondary Pb smelter was submitted to a batch leaching procedure (0.5–168 h) in 500 μM solutions of acetic, citric, or oxalic acids to simulate the release of toxic metals (Cd, Pb, Zn) in rhizosphere-like environments. Organic acids increased dissolution of fly ash by a factor of 1.3. Cadmium and Pb formed mobile chloro- and sulphate-complexes, whereas Zn partly present in a citrate (Zn–citrate −) complex is expected to be less mobile due to sorption onto the positively charged surfaces of hydrous ferric oxides (HFO) and organic matter (OM) in acidic soil.

Preliminary findings of chemistry and bioaccessibility in base metal smelter slags

Leaching of toxic metals from slag waste produced during smelting of Pb-Zn ores is generally considered to be negligible. A 1.4 million tonne stockpile of slag containing up to 2.5% Pb and other contaminants has accumulated on a smelter site at North Lake Macquarie, New South Wales, Australia, and it has also been freely used within the community for landscaping and drainage projects. It had been suggested that Pb in fine particles derived from the slags may be a potential contributor to the blood Pb of some children in this community, although there is conflicting evidence in the literature for such a hypothesis. Bioaccessibility of lead and selected metals derived from nine slag samples collected from areas of public open space was examined using a relatively simple in vitro gastric dissolution technique. Size analyses of the slag samples demonstrate that finely-sized material was present in the slags which could be ingested, especially by children. The finer-sized particles contain high levels of Pb (6,490-41,400 ppm), along with Cd and As. Pb bioaccessibility of the slags was high, averaging 45% for -250 microm material and 75% for particles in the size range -53+32 microm. Increasing bioaccessibility and Pb concentration showed an inverse relationship to particle size. Almost 100% of Pb would be bioaccessible in the smallest slag particles (<20 microm), which also contained very high Pb levels ranging from 50,000 to 80,000 ppm and thus constitute a potential health hazard for children.