Iron Contamination Research Articles

Inferring the distribution of iron oxidation species on mineral surfaces during grinding of base metal sulphides

Electrochemistry plays an important role in the flotation of base metal sulphide minerals. During grinding a galvanic interaction occurs between minerals and grinding media and controls the iron contamination on mineral surfaces, which depresses mineral flotation significantly. In this study, the galvanic interaction was quantified by measuring the iron oxidation species originated from grinding media by ethylene diamine-tetra acid (EDTA) extraction in single mineral and mixed mineral systems. It was found that the extent of galvanic interaction between minerals and grinding media was intimately associated with the electrochemical reactivity of minerals. The nobler the mineral, the stronger the galvanic interaction with grinding media, and the higher the amount of iron oxidation species from grinding media. For both galena and chalcopyrite a linear relationship was observed between the amount of iron oxidation species and flotation recovery in single mineral systems. This relationship was able to predict the iron oxidation species on galena and chalcopyrite surfaces when they were mixed with pyrite separately. The distribution of iron oxidation species onto the two minerals in the mixture changed with the ratio of the mineral surface areas and was correlated with mineral flotation recovery. The major cathodic mineral in the mixture was dictated by the combination of mineral surface area and reactivity and drew iron oxidation species from the grinding media.

Assessment of heavy metals concentrations in coastal sediments in north-western cities of Madagascar

This study was undertaken to evaluate the heavy metals contamination of copper, zinc, manganese, iron, chromium, nickel, lead and cadmium, to assess the environment quality of the coastal area from town activities. Nickel, lead and cadmium are used in different kind of current accumulators and they are dangerous for sea wild life and for human food resources. The five others metals are usual and at a high concentration they are able to threat environment system. Six samples had been choice at two town of Madagascar north-western coast: Nosy Be and Mahajanga, in February, 2007. These sampling points stand in front of each mean sewage mouths in each locality. Table 1 and 2 give us same descriptions of each sampling points. These two sampling area are among the principal fishing area of Madagascar. Three kinds of analytical method were used for metals determination and quantification: flame spectrophotometer atomic absorption, UV spectrophotometer, and voltammeter method. The flame spectrophotometer atomic absorption gives the best result by testing with certified reference materiel. Our data suggested that Mahajanga’s stations have higher values of cadmium (1 mg/kg) and lead (91 mg/kg) than the non-contaminated sediments. However, the concentrations of other metals such as copper, zinc, manganese, iron and chromium in Nosy Be sediments, were twice as higher than in those of Mahajanga. In compiling our data obtained at the same stations in the vertical water column, we would like to confirm the growing order of potential absorption between metals and sediments, nickel, copper, cadmium and lead. According to the results of determinations, we suggested that more determination should have done in open sea to assess metals in a wide scale. Key words: Marine pollution, heavy metals, coastal sediments, toxicity, Nosy Be, Mahajanga, Madagascar

Characterisation of Cutting Systems on Physical Processing of Spent Batteries

Laboratorial studies were carried out to characterise the influence of different cutting systems (grab shredder and cutting mill) on the physical processing efficiency of spent Zn-MnO2 batteries. The grab shredder operate based on an indented cutting rotor which applies shear and abrasion stresses with a moderate rotation speed, while the cutting mill operation is based on shear and impact stresses at higher rotation speed. After shredding with the grab shredder, two fractions of material were obtained (above and below the 6 mm discharge grid), which allows a previous separation of the scrap. With the cutting mill, all the grinded material passed the bottom grid (with the same 6mm opening). Results obtained showed that alkaline batteries were more efficiently shredded than saline batteries, mainly with the grab shredder. Average diameters (d50) for saline and alkaline batteries fragmented with the grab shredder were 2.29 and 1.47 mm respectively, while with the cutting mill were 3.09 and 1.54 mm respectively. Chemical analyses were carried out for different size fractions allowing identifying metals distribution through size categories. In general chemical composition was not substantially different using both shredding systems. Zinc distribution was almost constant with the grain size while manganese distribution decreased with particle size. More than 94% of the iron scrap from the battery cases presents a particle size higher than 1.4 mm using both cutting systems. Due to this result, it is possible to separate the scrap retained in the coarse fraction by sieving with the identified mesh. Maximum selectivity points, corresponding to the maximum separation of zinc plus manganese from iron, were also determined. Higher zinc and manganese recoveries were obtained with the grab shredder, despite iron contamination (20-25%) can be considered significant.

Two-side surface photovoltage studies for implanted iron diffusion in silicon during rapid thermal anneal

Two-side surface photovoltage (TS-SPV) based on measuring SPV from both wafer sides is proposed as the approach for silicon iron contamination monitoring. TS-SPV is applied to follow diffusion of implanted iron in a lightly doped p-type silicon during rapid thermal anneal (RTA). Good correlation is found between the iron distribution versus RTA conditions in the range of 375–1100°C. The impact of thermal donors in silicon after RTA at below 700°C is illustrated. The portion of iron detectable by SPV (FeB pairs) is found as a function of RTA time and temperature. Iron diffusion activation energy was evaluated for the interstitial ionized iron Fei+ and for the interstitial neutral iron Fei0. Low thermal budget RTA combined with TS-SPV has been proven to be an effective iron contamination monitor to identify contamination sources, character, and location.

The effect of iron contaminants on thiosulphate leaching of gold

Metallic iron and ferric ions were subjected to wet grinding with a sulphide ore in a ceramic ball mill to simulate the fine grinding process using mild steel, in an attempt to investigate the effect of iron species on the ammoniacal thiosulphate leaching of gold. Metallic iron and ferric ions decreased gold leaching in both kinetics and overall extraction when they were added in the wet grinding of a sulphide ore. This detrimental effect became more pronounced with the addition of metallic iron and ferric ions at higher concentrations. Metallic iron retarded the gold leaching more than ferric ions at the same dosage. The decomposition of thiosulphate in the leaching of the sulphide ore increased with the addition of metallic iron and ferric ions in the wet grinding. Thermodynamic analysis indicated that the predominant species for iron was ferric hydroxide under the leaching conditions. Wet grinding at a higher pH of 9 and use of ethylenediaminetetraacetic acid (EDTA) were ineffective in improving the gold leaching with the addition of metallic ions and ferric ions in the wet grinding. Iron oxide and hydroxide slime coatings at the surfaces of pyrite and pyrrhotite were reduced using carboxymethyl cellulose (CMC) to render the sulphide and slime particle surfaces highly negatively charged. Precipitation of iron oxide species at the surfaces of pyrite and pyrrhotite was observed in the morphological study of the leach residues with the addition of metallic iron in the wet grinding. The addition of CMC effectively reduced iron oxide slime coating at the sulphide surfaces and the aggregation of fine particles.

Synthesis, structure and sinterability of 6061 AA100−x–xwt.% TiO2 composites prepared by high-energy ball milling

Abstract Manufacturing of 6061 Al alloy reinforced with different weight percentages of TiO2 metal matrix composite powder through low-energy and high-energy ball milling for microcomposites and nanocomposites respectively followed by cold uniaxial compaction and sintering was investigated. The milled powder was characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and differential thermal analyzer. No intermetallic compounds were observed during high-energy ball milling by wet method, but petite iron contamination was present due to vial media after 40 h milling. The crystallite size of about 46 nm was obtained in the case of high reinforcement content. Powder surface morphology, crystallite size as a function of chemical composition and milling time, and lattice parameter of the high-energy ball-milled powder were examined. The effect of matrix-to-reinforcement particle size ratio on the green compressive strength for both composites was also investigated. The green pellets were degassed at 350 °C for 60 min, and then sintered in the temperature steps of 475, 550 and 625 °C under reducing atmosphere for 120 min. The effects of reinforcement content on densification as percentage theoretical density, sinterability and Vickers hardness of the composites were also studied. The results revealed that the sinterability improved as the percentage of reinforcement increased for nanocomposites whereas it worsened for microcomposites. The nanocomposites exhibited a high Vickers hardness of 1126 MPa, which was around 3–4 times higher than that of microcomposites.

Mechanical alloying, microstructure and properties of Nb–16Si alloy

Abstract Nb–16 at.% Si bulk alloys were prepared by uniaxial hot pressing from mechanically alloyed powder mixtures. It is shown that the addition of appropriate absolute ethyl alcohol significantly restrained the agglomeration of particles and accelerated the milling process. Moreover, besides the solid solution of Si into Nb lattice, significant iron contamination dissolved into Nb to develop another Nb solid solution after a long milling time. Sintering results indicate that, with sintering temperature increasing from 1200 to 1500 °C, densities and mechanical properties of sintered alloys increased and the morphology of constituent phases (niobium solid solution, Nb 5 Si 3 and Nb 3 Si in micron dimension) changed from irregular shape to nearly equiaxed one. However, as for the material hot pressed at 1600 °C, the microstructure became coarser and the properties were not improved because of the weakening of fine-grain contribution.

Lead, arsenic, fluoride, and iron contamination of drinking water in the tea garden belt of Darrang district, Assam, India

Drinking water quality with respect to lead, iron, fluoride, and arsenic has been carried out in and around tea gardens of Darrang district of Assam, India. The district lies between 26 degrees 25(') and 26 degrees 55(') northern latitude and 91 degrees 45(') and 91 degrees 20(') east longitude and covers an area of 3,465.30 km(2). Twenty-five different sampling stations were selected for the study. Iron, lead, and arsenic were analyzed by using an atomic absorption spectrometer, Perkin Elmer AA 200, while fluoride was measured by the SPADNS method using a UV-VIS spectrometer, Shimadzu 1240 model. The study revealed that the water sources in the area are heavily polluted with lead. Statistical analysis of the data is presented to determine the distribution pattern, localization of data, and other related information. Statistical observations imply non-uniform distribution of the studied parameters with a long asymmetric tail either on the right or left side of the median.

Investigation into the heap leaching of copper ore from the Disele deposit

Heap leaching of malachite–atacamite ores with high silica gangue using sulphuric acid is reported. The base metals were present in the ores in copper rich nodules with a network of fine strings rich in cobalt and manganese along the quartz grain boundaries. It was observed that leaching of copper was quicker and the corresponding recovery of copper was consistently higher when the ore particle was finer. The recovery of copper measured at different leaching times revealed that the efficiency of the process was better enhanced by refinement of the ore particle size than by increasing the concentration of sulphuric acid in the lixiviant from 60 to 120 g/L. Iron contamination in the pregnant leach solution (PLS) subsequently increased as the initial acid concentration in the lixiviant increased. The water loss during the heap leaching process was higher when the ore particle size was finer and when the concentration of sulphuric acid in the lixiviant was higher. Leaching residues typically contained 92% SiO 2 and 4% muscovite.

Investigation of iron impurity gettering at dislocations in a SiGe/Si heterostructure

This article examined the electrical activities of dislocations in a SiGe/Si heterostructure by deep level transient spectroscopy (DLTS) after iron contamination and phosphorous diffusion gettering. DLTS of iron contaminated samples revealed a peak at 210 K, which was assigned to individual iron atoms or very small (<2 nm) precipitates decorated along dislocations, considering that the iron contamination annealing was terminated by quenching and transmission electron microscopy did not reveal any precipitate at dislocations. Arrhenius plot of the 210 K peak yielded a hole capture cross section of 2.4×10−14 cm2 and an energy level of 0.42 eV above the valance band. The relatively large hole capture cross section indicates strong interactions between iron-related deep levels and the dislocation shallow bands. DLTS of the iron contaminated sample revealed that 6×1014 cm−3 of boron can more effectively trap interstitial iron at room temperatures than the strain field/defect sites at 107–108 cm−2 dislocations. Phosphorous diffusion experiments revealed that the gettering efficiency of iron impurities depends on the dislocation density. For regions of high dislocation density, phosphorous diffusion cannot remove all iron impurities decorated at dislocations, suggesting a strong binding of iron impurities at dislocation core defects.

Hydroxamate siderophore-promoted reactions between iron(II) and nitroaromatic groundwater contaminants

Recent studies show that ferrous iron (Fe II), which is often abundant in anaerobic soil and groundwater, is capable of abiotically reducing many subsurface contaminants. However, studies also demonstrate that Fe II redox reactivity in geochemical systems is heavily dependent upon metal speciation. This contribution examines the influence of hydroxamate ligands, including the trihydroxamate siderophore desferrioxamine B (DFOB), on Fe II reactions with nitroaromatic groundwater contaminants (NACs). Experimental results demonstrate that ring-substituted NACs are reduced to the corresponding aniline products in aqueous solutions containing Fe II complexes with DFOB and two monohydroxamate ligands (acetohydroxamic acid and salicylhydroxamic acid). Reaction rates are heavily dependent upon solution conditions and the identities of both the Fe II–complexing hydroxamate ligand and the target NAC. Trends in the observed pseudo-first-order rate constants for reduction of 4-chloronitrobenzene ( k obs, s −1) are quantitatively linked to the formation of Fe II species with standard one-electron reduction potentials, E H 0 (Fe III/Fe II), below −0.3 V. Linear free energy relationships correlate reaction rates with the E H 0 (Fe III/Fe II) values of different electron-donating Fe II complexes and with the apparent one-electron reduction potentials of different electron-accepting NACs, E H 1 ′ (ArNO 2). Experiments describing a redox auto-decomposition mechanism for Fe II–DFOB complexes that occurs at neutral pH and has implications for the stability of hydroxamate siderophores in anaerobic environments are also presented. Results from this study indicate that hydroxamates and other Fe III-stabilizing organic ligands can form highly redox-active Fe II complexes that may contribute to the natural attenuation and remediation of subsurface contaminants.

Sulphuric acid leaching of polymetallic nodules using paper as a reductant

Sulphuric acid leaching of manganese nodule for extraction of Cu, Ni, Co and Mn in presence of a novel cellulosic reductant, waste newspaper, has been reported. The various parameters chosen for the study were: time, temperature, H2SO4 concentration and amount of paper. To quantify the linear and interaction coefficients a 23 full factorial design of experiments was followed. The regression equations were determined and the adequacy of these equations was tested by Fischer’s test. The linear coefficients for time, acid concentration and amount of paper were found to be significant for extraction of Cu, Ni, Co and Mn. While acid concentration and amount of paper showed positive interactions for Cu, Ni and Co extractions it had negative significance for Mn dissolution. Under the conditions for >97% extraction of metal values iron extraction was ∼40%. In order to reduce the iron contamination by discarding iron as jarosite effect of addition of ammonium sulphate during leaching was also studied. Iron extraction could be brought down to 14% from ∼40% with the addition of 30g/L (NH4)2SO4 without affecting the recoveries of other metals.

Effect of internal gettering of iron on electrical characteristics of devices

Different types of gettering treatments were applied to a real device process to evaluate their ability to remove iron contamination from the device layer and improve the electrical characteristics of the devices. NMOS and PMOS transistors and other test structures were manufactured on boron doped, both iron contaminated and uncontaminated Cz silicon wafers with or without gettering treatment. Gettering treatments, which were designed to induce sufficient iron precipitate nucleation in the bulk to ensure iron precipitation, were inserted in the fabrication process after the last high temperature treatment in which the iron solubility was higher than the contamination level. The electrical characteristics of the devices, such as leakage currents, were measured. The applied gettering treatments were found to be inefficient to improve the device performance, possibly due to stronger gettering to heavily doped, ion implantation damaged device layer.

Electrical properties of n-type multicrystalline silicon for photovoltaic application—Impact of high temperature boron diffusion

The effects of boron diffusion were investigated on electronic grade n-type single- and multicrystalline silicon wafers for solar cells application. Doped p +-layers were formed using specific spin-on dopant (SOD) source annealed in a tube furnace. Homogeneous diffused layers with sheet resistance values of 70 Ω/sq were achieved on large area silicon wafers. Bulk electrical properties were investigated measuring the effective carrier lifetime after the diffusion step. A significant degradation of the bulk electrical properties was observed using the SOD technique. Unlike for the single-crystalline silicon, it was determined that this effect was not due to an interstitial iron contamination originating from the SOD, but rather by the thermal degradation of the material. Boron diffusion was followed by a phosphorous diffusion sequence, necessary in the fabrication process for the formation of the back surface field. This additional step leads to an improvement of effective lifetime values due to an efficient gettering of the impurities. Finally, bulk carrier lifetimes from 100 μs to over 300 μs were deduced on n-type multicrystalline silicon after boron and phosphorus diffusion. This underlines the potential of this material for photovoltaic application and its stability after high temperature treatments provided that a gettering step is included after the boron diffusion step.

Effect of iron in silicon feedstock on p- and n-type multicrystalline silicon solar cells

The effect of iron contamination in multicrystalline silicon ingots for solar cells has been investigated. Intentionally contaminated p- and n-type multicrystalline silicon ingots were grown by adding 53 ppm by weight of iron in the silicon feedstock. They are compared to reference ingots produced from nonintentionally contaminated silicon feedstock. p-type and n-type solar cell processes were applied to wafers sliced from these ingots. The as-grown minority carrier lifetime in the iron doped ingots is about 1–2 and 6–20 μs for p and n types, respectively. After phosphorus diffusion and hydrogenation this lifetime is improved up to 50 times in the p-type ingot, and about five times in the n-type ingot. After boron/phosphorus codiffusion and hydrogenation the improvement is about ten times for the p-type ingot and about four times for the n-type ingot. The as-grown interstitial iron concentration in the p-type iron doped ingot is on the order of 1013 cm−3, representing about 10% of the total iron concentration in the ingot, and is reduced to below 1011 cm−3 after phosphorus diffusion and subsequent hydrogenation. The concentration of interstitial iron after boron/phosphorus codiffusion and hydrogenation is about 1012 cm−3, pointing out the reduced gettering effectiveness of boron/phosphorus codiffusion. The effect of the iron contamination on solar cells level is a decrease in the diffusion length in the top half of the ingots with a trend in agreement with Scheil’s model for segregation. This is, however, not the only impact of the iron. An increased crystal defect concentration in the top and bottom of the Fe doped ingots, compared to the reference ingots, is observed, which contributes considerably to the degradation of the solar cell performance.

Feasibility study of SR‐TXRF‐XANES analysis for iron contaminations on a silicon wafer surface

AbstractThe ability to chemically characterize the contamination on silicon wafers is of critical importance to the semiconductor industry. It provides information on possible unwanted chemical processes taking place on the wafer surface and helps in determining the true source of the contamination problem. This type of information is not readily accessible with standard laboratory equipment. Synchrotron radiation‐induced total reflection X‐ray fluorescence (SR‐TXRF) was combined with X‐ray absorption near‐edge structure (XANES) to determine the chemical state of Fe contaminations on a silicon wafer surface. Main purpose of the study was to test the method for a contamination issue as it could appear in a microelectronic VLSI production fab. Copyright © 2008 John Wiley & Sons, Ltd.

Effect of the milling energy on the production and thermal stability of amorphous Mg50Ni50

The effect of milling energy on the amorphisation process and subsequent thermal crystallization of Mg50Ni50 was investigated. The amorphous Mg50Ni50 was produced using a planetary mill (medium energy) with a ball to material weight ratio of 13:1, and a SPEX mill (high energy) with a ball to material weight ratio of 20:1. The results obtained by means of X-ray diffraction showed that it is possible to obtain an amorphous Mg50Ni50 alloy, through both milling processes, starting of Ni powders and Mg turnings. However, the amorphisation process requires more time in the planetary mill (80–90 h) than in the SPEX mill (15–20 h), due to the difference in energy level and milling mechanism between these mills. The phase evolution during the amorphisation process is practically independent of the mill energy. In this way, it was observed that the mill conditions promoted an extensive refinement of the microstructure during the first hours of milling. The defects produced during this time led to the amorphisation of part of the system. This amorphous precursor suffers a mechanically induced crystallization into Mg2Ni, which is subsequently destabilized into amorphous Mg50Ni50. Based on the results obtained, it is proposed that the formation of amorphous precursor during mechanical milling of Mg and Ni is a characteristic of the Mg–Ni system, over a wide composition range, rather than of a particular composition. In relation to the thermal crystallization of the amorphous produced, the results of the differential thermal analysis applied to the amorphous samples showed that the formation enthalpy for both amorphous is the same, however, the amorphous produced in a planetary mill presented higher crystallization temperatures and apparent activation energies than the amorphous produced in a SPEX mill. The last behavior would be related with iron contamination coming from the erosion of the milling media. Finally, it is possible to conclude, that under the experimental condition employed, the amorphous phases produced in a planetary and SPEX mill, are structurally and energetically similar.

Influence of Fe/Cr on nitrogen doped carbon nanotube growth

Using electron energy loss spectroscopy in a 100 kV VG scanning transmission electron microscope we study nitrogen doped carbon nanotubes grown via electron cyclotron resonance (ECR) microwave plasma techniques. The process is controlled by direct current (dc) biasing the grid separating the ECR source and the substrate. We show that plasma induced sputtering of the ECR source wall (stainless steel) can lead to significant iron and chromium contamination of growth samples. We identify various Fe, Cr, Ni nitride phases, and propose a growth model based on nitridation-induced metal segregation of steel based FeCrN alloys. Trace Cr doping of nanotube catalysts appears a promising route for introducing large nitrogen concentrations into both single and multi-walled nanotubes and may accelerate nanotube growth rates.

Effect of transition metals on oxygen precipitation in silicon

Effects of iron and copper impurities on the amount of precipitated oxygen and the oxide precipitate and stacking fault densities in Czochralski-grown silicon have been studied under varying thermal anneals. Silicon wafers were intentionally contaminated with iron or copper and subsequently subjected to different two-step heat treatments to induce oxygen precipitation. The iron contamination level was 2 × 1013 cm-3 and copper contamination level 6 × 1013 cm-3. Experiments did not show that iron contamination would have any effect on the amount of precipitated oxygen or the defect densities. Copper contamination tests showed some indication of enhanced oxygen precipitation.

Capacitance transient study of the influence of iron contamination on the electrical characteristics of silicon grain boundaries

The influence of iron contamination on the electrical characteristics of an interfacial grain boundary created by bonding two (110)∕(100) silicon wafers was examined by a capacitance transient technique. Compared with the clean sample, iron contamination increases both the density of boundary states (by at least three times) and the zero-bias barrier height (by 70meV), while dramatically reducing by two orders of magnitude the electron/hole capture cross-section ratio. These results suggest that a larger barrier will be sustained at the iron contaminated boundary under low injection condition, thereby enabling more effective minority carrier collection and associated enhanced recombination activity.