Pyrite Cinder Research Articles

Influence of sulfur content in raw materials on oxidized pellets

The influence of sulfur content in raw materials on oxidized pellets was studied. The results show that most sulfur exists in the form of elementary sulfur in pyrite cinder, and over 95% sulfur is removed in producing pyrite cinder oxidized pellets. The compressive strength of fired pellets drops from 3 186 N to 2 405 N when the ratio of pyrite cinder increases from 40% to 70% under the conditions of preheating at 900 °C for 9 min and firing at 1 230 °C for 15 min. The porosity and microstructures of fired pellets prove that the higher ratio of pyrite cinder is given, and the more holes and cracks are achieved, leading to the better reducibility index (RI) and reduction swelling index (RSI), and the lower compressive strength of fired pellets and the worse reduction degradation index (RDI).

Hexagonal hematite platelets synthesized from pyrite cinders by hydrothermal process

Well-crystallized hexagonal hematite (α-Fe2O3) platelets were synthesized by hydrothermal process, using a highly concentrated ferric hydroxide as precursor. The precursor was prepared by adding ammonia to the ferric sulfate solution which was obtained by leaching pyrite cinders with sulfuric acid. Structure and morphology of the synthesized products were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscope and selected area electron diffraction. The results reveal that the reaction temperature has significant effects on the structure, size and shape of the synthesized hematite particles. Typical hexagonal hematite platelets, about 0.4–0.6 μm in diameter and 0.1 μm in thickness, were prepared at 230 °C for 0.5 h. Al3+, contained in the sulfuric acid leaching solution as an impurity, plays an extremely important role in the formation of hexagonal hematite. In addition, a possible mechanism about the formation of hexagonal hematite platelets was proposed.

Influence of microorganisms on arsenic mobilization and speciation in a submerged contaminated soil: Effects of citrate

Batch-type leaching experiments were performed on polluted soil contaminated by pyrite cinders to evaluate the effect of indigenous bacteria on arsenic mobilization. The bacteria, under submerged conditions using citrate as the carbon source, enhanced the solubilization of arsenic, iron and manganese. At the same time, 85 mg kg −1 of copper were abiotically released. Iron reduction significantly ( p < 0.05) enhanced the release of arsenic. During 7 days of incubation at high redox potential, the arsenite content increased suggesting aerobic arsenic-resistant bacteria bearing arsC genes as key players for arsenate reduction. Arsenate became prevalent in consequence of arsenic liberation from iron oxides and the lowering of redox potential, driven by citrate, inhibited the growth and activity of arsenate-resistant bacteria. Populations of Bacillus, Pseudomonas, and Geobacter were stimulated by the addition of citrate as evidenced by denaturing gradient gel electrophoresis analysis of 16S rRNA genes. Putative ars genes were retrieved in isolates of Bacillus and Pseudomonas. These isolates were able to reduce 2 mmol l −1 of arsenate in liquid cultures. These results confirm that microorganisms play an important role in As cycling in soils and highlight the complex role of citrate on biotic and abiotic transformations of inorganic contaminants. The environmental dispersion of arsenic can be retarded by resorption or coprecipitation processes occurring during flooding. Nevertheless, periodic flooding can be a crucial factor for the groundwater quality and the soil–water–plant systems.

Thermomechanical studies of ceramic tile made from technogenic raw materials

The studies described make it possible to judge the strain – stress state of ceramic articles at different stages of firing and to establish their effect on the thermomechanical properties of the material. The studies showed that the introduction of pyrite cinders into ceramic paste lowers the elastic modulus by 25 – 30% during the initial period (to 400°C) and 4 – 10% in the temperature interval 500 – 1000°C. These data show that pyrite cinders can be used to intensify firing.

Preparation, morphology and coagulation characteristics of a new polyferric chloride coagulant prepared using pyrite cinders

Pyrite cinders are the main industrial waste generated from the process of sulphuric acid production using pyrite ores. The pyrite cinders may have utilization value in preparing a new polyferric chloride (PFC) coagulant. In order to attain this objective, a preparation method for PFC products from pyrite cinders was studied by a Taguchi orthogonal array experiment. On the basis of the successful preparation, the morphologies and coagulation characteristics of three PFC products, with different basicities, were observed by transmission electron microscopy (TEM) and examined by jar tests, respectively. The results showed that the molar ratio of NaOH to Fe should be in a range between 0.75:1 and 1:1, the molar ratio of stabilizer NaH2PO4 to Fe should be in a range between 0.12:1 and 0.15:1, the curing time should be 2 h, the curing temperature can be 60 °C and the molar ratio of NaHCO3 to Fe can be determined according to the basicity required in order to get the optimal stability of PFC products and the best flocculation efficiency. Although the degree of aggregation of the PFC products became larger with the increase in the basicity, the coagulation efficiency could be only improved with an increase in the basicity within a certain range. When the basicity exceeded a certain value, the coagulation efficiency started to decrease. In this study, PFC2 (B = 11.16%) had better coagulation characteristics than either PFC1 (B = 6.08%), PFC2 (B = 11.16%), PFC3 (B = 15.92%) or polyaluminium chloride (PAC).

Risk-based assessment of multimetallic soil pollution in the industrialized peri-urban area of Huelva, Spain

The peri-urban soils of Huelva, one of the first industrial cities in Spain, are subject to severe pollution problems primarily due to past poor management of industrial wastes and effluents. In this study, soil cores were collected in seven sites potentially contaminated with toxic chemicals arising from multiple anthropogenic sources, in order to identify trace elements of concern and to assess human health risks associated with them. In most soil core samples, total concentrations of As (up to 4,390 mg kg(-1)), Cd (up to 12.9 mg kg(-1)), Cu (up to 3,162 mg kg(-1)), Pb (up to 6,385 mg kg(-1)), Sb (up to 589 mg kg(-1)) and Zn (up to 4,874 mg kg(-1)) were by more than one order of magnitude greater than the site-specific reference levels calculated on the basis of regional soil geochemical baselines. These chemicals are transferred from the hazardous wastes, mainly crude pyrite and roasted pyrite cinders, to the surrounding soils by acid drainage and atmospheric deposition of wind-blown dust. Locally, elevated concentrations of U (up to 96.3 mg kg(-1)) were detected in soils affected by releases of radionuclides from phosphogypsum wastes. The results of the human health risk-based assessment for the hypothetical exposure of an industrial worker to the surface soils indicate that, in four of the seven sites monitored, cancer risk due to As (up to 4.4 × 10(-5)) is slightly above the target health risk limit adopted by the Spanish legislation (1 × 10(-5)). The cumulative non-carcinogenic hazard index ranged from 2.0 to 12.2 indicating that there is also a concern for chronic toxic effects from dermal contact with soil.

Effect of Fe(II) on the formation of iron oxide synthesized from pyrite cinders by hydrothermal process

The effect of Fe(II) on the formation of iron oxide particles, synthesized from pyrite cinders lixivium via hydrothermal process, is investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The results indicate that Fe(II) can significantly affect the formation of iron oxide particles and the properties of the synthesized iron oxide particles. When n Fe(II)/n Fe(III) varies from 0 to 0.1, all the samples are crystallized to hematite (α-Fe 2O 3), without any other phase. Particle size of the prepared hematite gradually increases with the increase of n Fe(II)/n Fe(III) ratio, while the shape of the prepared hematite changes from sphere into platelet. When the n Fe(II)/n Fe(III) increases to 0.12, both α-Fe 2O 3 and Fe 3O 4 are formed and the shape of the product becomes spherical. As for the formation mechanism, it is found that Fe(II) can accelerate the phase transformation. The transformation process without Fe(II) is dissolution re-precipitation. However, in the transformation process with trace Fe(II), the phase transformation is dominated by solid-state transformation, though dissolution re-precipitation is still function. In addition, the formation of platelet-type hematite particles is attributed to that Al 3+ ions are adsorbed onto {0001} face.

Micaceous iron oxide prepared from pyrite cinders by hydrothermal method

Micaceous iron oxide (MIO) with a hexagonal flaky shape was prepared by hydrothermal method. The ferric hydroxide used as precursor was obtained by an acidic leaching solution of pyrite cinders reacting with ammonia solution. The optimal experimental conditions for preparing micaceous iron oxide were investigated by orthogonal experiments. Micaceous iron oxide can be successfully prepared when optimal parameters of total iron concentration of 2.0 mol/L, pH value of 8, n(Fe2+)/n(Fe3+) of 0.1, mass of seed crystal of 1 g, reaction temperature of 260 °C and reaction time of 30 min are applied. X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffractometry (SAEM) were adopted to characterize the hydrothermal products prepared under optimal conditions. The results indicate that highly crystallized α-Fe2O3 hexagonal flakes, about 1.0–1.5 μm in diameter and 0.1 μm in thickness, are prepared. Furthermore, the quality of micaceous iron oxide prepared can meet the required characteristics of micaceous iron oxide pigments for paints (ISO10601—2007).

Preparation of monodispersed micaceous iron oxide pigment from pyrite cinders

In this study, pyrite cinders are used as a second raw material for preparing micaceous iron oxide (MIO) pigment by leaching, precipitation and hydrothermal treatment. The optimal conditions for MIO synthesis, such as NaOH concentration, total iron concentration, reaction temperature and reaction time are investigated and discussed carefully, using pigment color and morphology as the major evaluation parameters. In addition, the synthesized products have been characterized by means of XRD and SEM/EDS. Under optimum conditions, the obtained MIO is uniform flake, metallic gray, and its mean particle size and aspect ratio are ~7.0μm and ~7.0. A scale-up experiment demonstrates its reproducibility. Besides, all the resulting products fulfill ISO 10601-2007, the standards of micaceous iron oxide pigments for paints.

Recovery of iron oxide concentrate from high-sulfur and low-grade pyrite cinder using an innovative beneficiating process

A high quality iron oxide concentrate, suitable as a feed for blast and electric reduction furnaces was recovered from high-sulfur and low-grade pyrite cinder. Pyrite cinder was treated with a hot strong alkali solution which dissolved most of the silica and alumina, leaving a solid residue and forming a precipitate which was an acid-soluble salt of aluminosilicate hydrate. The residue and precipitate were then treated with a diluted aqua regia to dissolve the precipitate and other impurities. Impurities such as the soluble silicates, aluminates and heavy metals can be extracted and produced high value-added products with several simple methods in later research. After analyzing the chemical composition and crystalline phase of raw material, the effects of different parameters on recovery efficiency of iron were carried out. The optimum reaction parameters were proposed as the following: melting at 200 °C for 1.0 h with 3.0 M NaOH in a liquid–solid ratio of 1.0:1.2 at atmospheric pressure, followed by leaching with aqua regia solution (3.0 vf.%) in a ratio of liquid-to-solid of 1.2:1.0 at room temperature for 1.5 h. In optimum parameters mentioned above, the raw residue only containing 38% Fe could be purified to about 65% and the recovery yield of Fe was 86%. Furthermore, the sulfur content of product could be reduced to 0.090% from 8.0%. To reveal the mechanism of this process, the phase transformation and microstructure of the process were studied by XRD and SEM with EDS.

Speciation analysis of metals (Tl, Cd and Pb) in Tl-containing pyrite and its cinder from Yunfu Mine, China, by ICP-MS with sequential extraction

The speciation of heavy metals such as thallium, cadmium and lead existing in pyrite and pyrite cinder was analyzed by ICP-MS with a sequential extraction procedure. The distribution patterns of these metals including exchangeable, reducible, oxidizable and residual fractions were obtained. Tl, Cd and Pb in pyrite and pyrite cinder samples from each extraction step were determined by inductively coupled plasma mass spectrometry (ICP-MS). Under the optimized instrumental conditions, detection limits of Tl, Cd and Pb in different matrices were within the range of 0.006–0.07 μg/L, and the relative standard deviations ranged from 0.8% to 1.2%. The accuracy of Tl, Cd and Pb determination was checked by analyzing two certified reference materials. The results demonstrate that trace Tl, Cd and Pb in the samples can be accurately determined. The sequential extraction results revealed that the percent contents of Tl, Cd and Pb in exchangeable, reducible and oxidizable fractions in pyrite cinder are different from those in pyrite and in pyrite cinder. Tl, Cd and Pb mostly are distributed in residual fraction. Therefore, the mobility of metals in pyrite is higher than that in pyrite cinder. Although distributions of Tl, Cd and Pb in the non-residual fraction are not dominant in pyrite cinder, the total concentrations of them could not be ignored. Consequently, attention must be paid to the risk of potential pollution by pyrite cinder.

Impact of glucose on microbial community of a soil containing pyrite cinders: Role of bacteria in arsenic mobilization under submerged condition

Arsenic transformation and mobilization in a pyrite cinder-polluted soil were studied under submerged conditions both in the presence and absence of glucose. The presence of the carbon source enhanced bacterial activity and a reduction in the redox potential, resulting in release of higher amounts of arsenic iron and manganese in the aqueous phase. Since arsenic solubilization was not concomitant to that of iron, desorption rather than dissolution was found to be the main mechanism controlling its release from pyrite cinders. Arsenate was reduced to arsenite whose presence increased during the time course of the experiment. Denaturing gradient gel electrophoresis analysis of 16S rRNA genes of the total bacterial community revealed that the addition of glucose stimulated uncultivable populations of Flavobacterium and Paenibacillus. The isolation technique enabled the characterisation of nineteen arsenic-resistant bacteria, mostly related to the facultative aerobic genera Bacillus, Paenibacillus, Staphylococcus and to Rhodococcus and Micromonospora. Most of them contained putative arsenate reductase and/or arsenite efflux pump as indicated by the presence of ArsC and/or ArsB genes. Four strains showed the ability to reduce arsenate by an intracellular detoxification mechanism, and one strain was able to oxidize arsenite, indicating that bacteria with the ability to oxidize or reduce arsenic are ubiquitous in soils. The findings confirm that bacterial activity was responsible for the arsenic reduction causing the solubilization of the metalloid from pyrite cinders to aqueous phases. Reducing conditions, such as those present in flooded soils in the presence of readily utilizable carbon sources could induce arsenic mobilization.

Humic acids affect root characteristics of fodder radish (Raphanus sativus L. var. oleiformis Pers.) in metal-polluted wastes

In a series of pot trials, fodder radish (Raphanus sativus L. var. oleiformis Pers.) was cultivated in pyrite cinders heavily polluted by various heavy metals (HM). The effects of application of humic acids (HA) to the cultures were evaluated at various concentrations (0.1 and 1 g kg−1 of cinders) and for different methods of application (mixed with cinders before sowing; applied on the top of substrate after sowing; foliar spraying), in comparison with untreated controls. HA increased the bioavailability of various HM, especially when applied at high concentrations. Low concentrations of HA, either mixed with cinders or applied on foliage, slightly enhanced shoot growth. High levels of HA were generally phytotoxic, probably because of the ensuing higher heavy metal concentrations in the shoots. Foliar spraying was partially able to attenuate the phytotoxicity of high dosages of HA, as revealed by the increased rate of leaf expansion. A negative correlation was found between shoot biomass and concentration of HM, and higher removals were generally associated with smaller doses of HA and foliar application. Within the range of concentrations tested, humic substances led to a reduction in root diameter and an increase in specific root length (SRL, length per unit weight of roots), significant only at the highest dosage, together with a tendency towards enhancement of translocation of HM to the shoot – both positive traits for phytoremediation purposes.

Potential use of pyrite cinders as raw material in cement production: Results of industrial scale trial operations

Pyrite cinders, which are the waste products of sulphuric acid manufacturing plants, contain hazardous heavy metals with potential environmental risks for disposal. In this study, the potential use of pyrite cinders (PyCs) as iron source in the production of Portland cement clinker was demonstrated at the industrial scale. The chemical and mineralogical analyses of the PyC sample used in this study have revealed that it is essentially a suitable raw material for use as iron source since it contains >87% Fe 2O 3 mainly in the form of hematite (Fe 2O 3) and magnetite (Fe 3O 4). The samples of the clinkers produced from PyC in the industrial scale trial operation of 6 months were tested for the conformity of their chemical composition and the physico-mechanical performance of the resultant cement products. The data were compared with the clinker products of the iron ore, which is used as the raw material for the production Portland cement clinker in the plant. The chemical compositions of all the clinker products of PyC appeared to conform to those of the iron ore clinker, and hence, a Portland cement clinker. The mechanical performance of the mortars prepared from the PyC clinker was found to be consistent with those of the industrial cements e.g. CEM I type cements. It can be inferred from the leachability tests (TCLP and SPLP) that PyC could be a potential source of heavy metal pollution while the mortar samples obtained from the PyC clinkers present no environmental problems. These findings suggest that the waste pyrite cinders can be readily used as iron source for the production of Portland cement. The availability of PyC in large quantities at low cost provides further significant benefits for the management/environmental practices of these wastes and for the reduction of mining and processing costs of cement raw materials.

Phytoremediation of soils polluted by heavy metals and metalloids using crops: (ii) early results from the in situ experiment of torviscosa (udine)

Two annual high biomass yield crops &ndash; Sorghum bicolor and Helianthus annuus &ndash; were grown in a soil polluted by pyrite cinders. Specific aims of this work were: to observe the concentration of metals in plants during the crop cycle and to establish the amount of metal removal by the crops. The field trial was arranged in a randomized block design. The concentrations of heavy metals in the soil were: As 309, Cd 4.90, Co 50.9, Cu 1527, Pb 233 and Zn 980 mg kg-1. The crops received respectively mineral fertilization and organic amendment while plants in control soil did not receive any input. The phytoextraction potential of crops was estimated during the whole growth cycle; the concentration of the metals in the plant roots and in the harvestable biomass and two bioconcentration factors are reported. The amelioration of the nutritive status of soil resulted highly effective for the biomass yield but not in the concentration of metals in plant fractions. The evaluation of the potential of phytoremediation of our plants compared to other crops in terms of metal removal, was positive. Sorghum performed better than sunflower removing from the soil 220 g ha-1 of As, 5.6 g ha-1 of Cd, 30.2 g ha-1 of Co, 820 g ha-1 of Cu, 107 g ha-1 of Pb and 1944 g ha-1 of Zn.

The application of phytoremediation technology in a soil contaminated by pyrite cinders

A research project dealing with the phytoremediation of a soil polluted by pyrite cinders is currently running. The case study is represented by a polluted area located in an industrial site; since 2001, the site has been listed in the clean-up national priority list. Before the beginning of the in situ trials, two experiments in controlled conditions were carried out. The first pot experiments were performed growing Glycine max, Sorghum bicolor, Zea mays and Helianthus annuus on substrates polluted by different levels of pyrite cinders, containing As, Cd, Cu, Pb and Zn. In a second experiment, the possible influence of fertilization on the uptake of As and heavy metals by S. bicolor and H. annuus was observed. The potential of phytoextraction of crops was evaluated considering the plant biomass, the concentration of As and heavy metals in the plant tissues and also the bioconcentration factor (BCF) and the translocation factor (TF). In the most polluted substrate, S. bicolor appeared more efficient than H. annuus in the uptake of metals; the transport of the metals from roots towards stems and leaves was less efficient in S. bicolor.

Removal of trace metals by Sorghum bicolor and Helianthus annuus in a site polluted by industrial wastes: A field experience

Using the perspective of full scale application of phytoremediation techniques, research is focusing on the optimization of agronomic practices. Two annual high biomass yield crops, Sorghum bicolor and Helianthus annuus, were grown in a polymetallic soil. The experimental site, polluted by pyrite cinders, is located in an industrial site that has been listed in the clean-up national priority list since 2001. Specific aims of this work were to observe the concentration of metals in plants during the crop cycle and to establish the amount of metal removed by the crops. The field trial, arranged in a randomized block design, started in 2005. The concentrations of heavy metals in the soil were: As 309, Cd 4.29, Co 50.9, Cu 1527 and Zn 980 mg kg −1. The crops grown on the polluted soil received mineral fertilization (Fert) and organic amendment (Org), while plants in control soil (Ctrl) did not receive anything. The plots were watered during the crop cycle during two drought periods, using a sprinkler irrigation system. The phytoextraction potential of crops was estimated during the whole growth cycle and the plant biomass that was collected in each sampling date was ICP-analyzed. Plant–biomass growth curves were obtained. The concentrations of the metals in the shoots and in the total plant biomass were recorded. Finally, the metal removal was calculated for the harvestable parts of the crops. The amelioration of the nutritive status of the substrate that resulted, was highly effective for the biomass yield. However, fertilization and soil amendment did not heighten the concentration of metals in the harvestable tissue of the plants during the crop cycle. In some cases, organic matter appeared to bind the elements making them less available for the plants. The evaluation of the potential of phytoremediation of our plants compared to other crops in terms of metal removal was positive. Our results of metal removal are consistent with the results from other in situ experiments. The Zn removal by S. bicolor and H. annuus reached about 2000 g ha −1 and 1000 g ha −1, respectively.

Technical properties of roof tiles made of technogenic material with pyrite cinder

It is demonstrated that introducing up to 15% pyrite cinder into ceramic mixtures significantly improves the cold resistance of roof tiles; the decrease in water absorption in this case is not proportional to the increase in cold resistance. Auniform distribution of pores of size 10−6–10−7 m facilitates a substantial increase in cold resistance.

Hazard assessment to workers of trace metal content in pyrite cinders.

Hazard assessment to workers of trace metal content in pyrite cinders.

In situ capping design of a pyrite cinder pile in the St. Lawrence river for metal containment

AbstractA pile of pyrite cinders discharged from a former manufacturing facility rest upon the bottom of the St. Lawrence River adjacent to Clark Island. In situ capping was the selected remedy to control both the fine particle resuspension that produced a red mud cloud in the water, commonly formed on windy days, and the soluble metals concentrations originating from the pyrite pile. Metal mass balances around the pile allowed estimates of the pre‐capping release rates. Elevated concentrations above the pile were observed for eight metals; these included iron, lead, mercury, selenium, arsenic, copper, cadmium, and zinc. After iron, the highest concentration in the pyrite particles were cadmium and zinc present in the 1,000 mg/kg range. Mercury was the lowest at the 10 mg/kg level in the pyrite solids. For iron the soluble release rate was estimated to be 0.08 g/s, and the particle release was 0.8 to 1.2 g/s. A 30 cm cap consisting of particles 19 to 40 mm in diameter is proposed for the site. Its placement covers a ten‐hectare area and is expected to isolate the fine pyrite particles and prohibit their resuspension into the water column. Design estimates of steady state flux reduction efficiencies range from a low of 99.21 percent for iron to a high of 99.96 percent for copper. Breakthrough times to achieve these steady state flux reductions range from 100 to 3,800 years and metal porewater concentrations at 5 cm below the cap surface are estimated to be reduced by 83 percent. Although soluble metals will continue to be released from the pile zone, the flux of all the metals will be significantly reduced. © 2002 Wiley Periodicals, Inc.