Chromium and nickel distribution in soils, active river, overbank sediments and dust around the Burrel chromium smelter (Albania)

Chromium ore was treated to produce ferrochromium from 1979 until 2000 in a smelter in Burrel, 35 km NE of Tirana (Albania). As a consequence, large amounts of solid waste, i.e. slags (about 9.10⁶ m³) have been disposed next to the smelter, disfiguring the landscape. In an attempt to define contaminated sites, heavy metal content of the different sampling media have been compared with respective background samples.In the study area, the determination of background values in soil samples is complicated due to the different geological substrates. Cr and Ni background concentrations in serpentinite-derived soils, west of the smelting plant, are markedly higher than in the Pliocene gravel/sandy soils, where the smelter is situated (Cr 2147 and 193 mg/kg, respectively; Ni 2356 and 264 mg/kg). These values are clearly lower than those encountered around the smelter. Average total Cr and Ni concentrations in soils around the smelter are 3117 and 1243 mg/kg, respectively. The highest concentrations of Cr (up to 2.3 wt.%), were recorded in samples taken near the smelting compartment within the industrial plant and next to the slags clearly indicating that the smelter forms a point source of Cr contamination. The Cr / Fe ratio is the best indicator to differentiate non-polluted (Cr / Fe Serpentinite soil: 130–390; Pliocene soils: < 130) from polluted areas (> 390 smelting nearby of the slags).Cr and Ni values for local backgrounds in stream and overbank sediments were taken in the Mat river 6 km upstream and to the east of the smelter (268 and 430 mg/kg for Cr, and 306 and 604 mg/kg for Ni, respectively). Equivalent sediments taken from the Zalli i Germanit river, which drains the smelter area are respectively 816 and 1126 mg/kg for Cr and 1115 and 1185 mg/kg for Ni.Dust samples, taken from the lofts of houses up to 2 km from the smelter, display high concentrations of Cr, Ni and Zn (average contents of 2899, 436 and 902 mg/kg, respectively). The later concentrations in the dust samples have been confirmed by mineralogical analysis where Cr-bearing mineral phases such as ferrochromium and chromium oxides, clearly relate to the activity of the smelter. Consequently, atmospheric deposition of dust particles forms a serious problem and can also be responsible for the elevated contents encountered in soil samples around the smelter.All these data show that the degree of contamination caused by industrial activity of the Burrel Cr-smelter is severe, although no Cr(VI) was detected in soil water extractions nor in the surface or groundwater where concentrations were < 0.01 mg/kg.     

Toxicity of Substances to Activated Sludge – Course of Inhibition Curves

A method is described for determining the course of inhibition curves substantiating the influence of some inorganic (Cr (VI)) and organic substances (phenol, synthetic tanning agents) on respiratory activity of heterogeneous biomass (activated sludge). Presented results prove that calculated inhibition curves have the course of a normal distribution function.     

不同海产动物和烟台海域不同海区的紫贻贝（Mytilus edulis）对重金属（Cr）富集的研究

产于烟台的５种海产经济动物对Ｃｒ的富集存在明显差异。底栖的滤食性贝类（紫贻贝Ｍ．ｅｄｕｌｉｓ、栉孔扇贝Ｃｈｌａｍｙｓｆａｒｒｅｒｉ、菲律宾蛤仔Ｒｕｄｉｔａｐｅｓｐｈｉｌｉｐｐｉｎｅｎｓｉｓ）的富集量远远超过自游泳的种类（中华马鲛Ｓｃｏｍｂｅｒｏｍｏｒｕｓｓｉｎｅｎｓｉｓ，长额七腕虾Ｈｅｐｔａｃａｒｐｕｓｐａｎｄａｌｏｉｄｅｓ）。紫贻贝为理想的海洋重金属Ｃｒ污染的指示动物．烟台海域各海区紫贻贝体内Ｃｒ含量最高，向边远海区逐渐降低。５种海产动物体内Ｃｒ的含量均在食品允许范围之内。     

Seasonal changes in speciation of dissolved chromium in the surface Sargasso Sea

The concentrations of Cr (III) and Cr (VI) were determined in the upper 500 m of the Sargasso Sea at different times of the year. Total Cr concentrations ranged between 2.5 and 4.5 nM, and the predominant species of Cr was the thermodynamically favoured Cr (VI). Cr (III) concentrations were greatest during periods of high biological activity, as indicated by strong correlations between the ratio of Cr (III):Cr (VI) and both bacterial biomass and primary productivity. Whilst the oxidation state varied substantially over the seasonal cycle, the upper water column inventory of Cr was relatively constant. The long residence time of Cr in the surface Sargasso Sea estimated with respect to atmospheric inputs (1410–2240 years) is indicative of the largely conservative behaviour of this element. Deep particle fluxes of Cr are similar or somewhat greater than atmospheric inputs, and this downward flux of Cr is well correlated with organic carbon fluxes from the upper Sargasso Sea. The long residence time coupled with the seasonal changes in oxidation state of Cr implies rapid seasonal recycling of Cr between redox states, with only slow removal via particles to the deep ocean at this site.     

High-pressure crystal chemistry of chromous orthosilicate, Cr2SiO4. A single-crystal X-ray diffraction and electronic absorption spectroscopy study

The high-pressure behaviour of chromous orthosilicate, Cr₂SiO₄, has been studied by means of single-crystal X-ray diffraction and electronic absorption spectroscopy. X-ray diffraction data show that the structure remains orthorhombic to the highest pressure reached of 9.22?GPa. The compressibility of the unit-cell is strongly anisotropic with the c axis approximately six times more compressible than the a and b axes. A third-order Birch-Murnaghan equation of state fitted to the volume-pressure data yields V ₀?=?610.10(3)?ų, K = 94.7(4)?GPa, K′?=?8.32(14). Cr₂SiO₄ is therefore more compressible than the isostructural Cd analogue, even though its molar volume is smaller. This unusual behaviour can be attributed to the fact that the Cr atom is too small for the six-coordinated site that it occupies, and the site is therefore strongly distorted. Structure refinements indicate that under high pressures the Cr atom remains strongly displaced from the central position of the octahedron. Polarized and unpolarized electronic absorption spectra include a strong absorption band occuring at 18.300 cm^?1 for E//c (which is parallel to the shortest Cr-Cr vector in the structure) which has an unusually large half width (5000?cm^?1), indicative of electronic interaction between metal centres. Deconvolution of unpolarized high-pressure spectra show that the relative integrated intensity of this component increases linearly from 40% at 1?bar to 60% at 11.2?GPa. Both the structural changes and the absorption spectra at high pressures suggest that pairs of adjacent Cr atoms in chromous orthosilicate form chromium dimers with a weak metal-metal bond, which is consistent with the diamagnetic response found at ambient pressure.     

Treating Leather Tanning Wastewater with Stone Cutting Solid Waste

This paper presents a new environmental approach for reducing environmental impacts of two local Palestinian industries: It implements the principle of “treating waste by waste.” The technical feasibility of chromium removal from wastewater in leather making by its treatment with solid waste from stone cutting industry is demonstrated experimentally, and found to be an efficient approach. Nearly full removal of chromium is obtained at optimum operating conditions using sufficient mass of solid waste (limestone) and allowing enough contact time between the two wastes. This study investigated effects of various parameters on the percentage relative decrease in concentration by using ultra violet (UV)/Vis spectrophotometry. Kinetic curves showed that percentage relative decrease in concentration increased with time until approaching a plateau (adsorption capacity). The adsorption capacity increased with increasing limestone to liquid ratio (solid content), until nearly full removal of chromium was obtained when the solid content was 5 g/100 mL or higher. This was accomplished within few days when the particles were settled. The adsorption capacity was pH dependent; adsorption at pH < 5 was obtained, as a finding which was not reported by previous investigators for Cr(III) adsorption using other particles. The percentage removal was nearly doubled at higher pH values (>5). Further research work is proposed to distinguish between the contributions of the two removal mechanisms of precipitation and adsorption.     

Luminescence spectroscopic study of Cr3+ in Brazilian topazes from Ouro Preto

In this paper, the results of investigation of luminescent properties of topazes from Ouro Preto, Brazil are presented. It is established that all photoluminescence characteristics of variously colored topazes are due to three structurally non-equivalent Cr³⁺ centers isomorphically substituting Al³⁺ in the topaz structure and forming [CrO₄F₂]⁷⁻, [CrO₄OH,F]⁷⁻, and [CrO₄(OH)₂]⁷⁻ complexes. Kinetics of thermal annealing indicates different thermal stability of these centers. Less stable [CrO₄OH, F]⁷⁻- and [CrO₄(OH)₂]⁷⁻ complexes diminish in temperature range 950–1,100°C, accompanied by appearance of corundum phase. The most stable [CrO₄F₂]⁷⁻ centers completely decay at 1,250°C and luminescence spectrum of product obtained becomes identical to that of Cr³⁺ in mullite indicating that topaz completely transforms to mullite.

Chromium contamination from chromite mine

Among the dominant species of chromium, the trivalent form widely occurs in nature in chromite ores or in silicate minerals and is extremely immobile. The higher oxidation state Cr(VI), is, however, rarely found in nature, is more mobile, and several times more toxic than Cr(III). Cr(VI) occurs in chromates and dichromates manufactured from chromite ores. The hexavalent state is stable in an oxidizing alkaline environment, whereas the trivalent state is stable in a reducing acidic environment. Serpentinization and Mg release during deuteric alteration of ultramafic rocks create alkaline pore water and lateritization is an intensive oxidation process. Chromite ore bodies in oxidized serpentinite therefore may generate hexavalent chromium from the inert chromites and cause hazardous chromium pollution of the water. With this end in view, a combined field and laboratory study has been made on chromite-bearing oxidized serpentinite rocks of Sukinda in Orissa, India. Laboratory leaching studies on mine overburden samples, chemical analyses of streamwater, and hydrolysate incrustation on detrital grains taken from stream beds have indicated the possibility of chromium mobilization from the chromite ores into the waterbodies.     

The Geochemical Effects of Microbial Humic Substances Reduction

As part of a study on microbial redox alteration of humic substances we investigated the potential effect of this metabolism on the fate of heavy metals and hydrocarbons as a result of conformational alteration of the humic molecular structure due to microbial reduction. Our studies indicate that the microbial reduction of humic acids (HA) results in significant morphological and geochemical alterations. X‐ray microscopy analysis indicate that the conformational structure of the humic colloids is altered as a result of the redox change. In the reduced state, the HA appeared as small dense particles, on reoxidation, large loose aggregates were formed. In addition, spectrofluorometric studies indicated that the binding capacity of the HA for naphthalene was decreased by 10% when the HA was reduced. Similarly, the reduced HA yielded higher surface tension values at all concentrations tested which is indicative of a more hydrophilic and less hydrophobic solute. On reoxidation, the surface tension values reverted back to values similar to those obtained for the untreated oxidized HA. These data indicate that the hydrophobicity of the HA is altered on biological reduction of the HA and that this alteration is reversible. In contrast the reduced HA demonstrated a 15% higher affinity for heavy metals such as divalent cobalt than the oxidized HA. In addition to increasing the binding capacity of HA for heavy metals, the reduction of the HA also decreased the bioavailability and toxicity of bound heavy metals such as chromium. When incubated in the presence of Cr(III) and HA, cells of Escherichia coli grew much more rapidly in the presence of the reduced HA suggesting that the higher metal binding capacity of the reduced humic substances resulted in a removal of the Cr(III) from solution and hence reduced its bioavailability and toxicity. These studies demonstrate that HA redox state and reduction of humic acids by microorganisms can have a significant effect on the molecular morphology and binding constants of HA for heavy metals and hydrocarbons and also directly affects the bioavailability of these compounds in the environment.     

Chromium(VI) distributions in the Arctic and the Atlantic Oceans and a reassessment of the oceanic Cr cycle

Chromium(VI) concentrations ranging between 3.0 and 6.1 nmol l⁻¹ and 3.1 and 7.3 nmol l⁻¹ were found in the Arctic and Atlantic Oceans, respectively. The vertical profiles show modest depletion of chromium(VI) in surface waters, but poor overall correlations between Cr(VI) and nutrient profiles. Given that Cr(VI) is the dominant oxidation state of chromium in open-ocean waters, these data are combined with literature data to reassess the distribution of Cr in oceanic waters. It is concluded that while Cr shows some characteristics of both “recycled” and “accumulated” vertical profiles, it does not fall clearly within either group.