With chromium concentration

It is clear from the data in Table 4.6 that the corrosion rates increase with increase in chromium in sulfuric acid solution. The presence of 10% Ni in the Fe-Cr alloy results in decreasing corrosion rate with chromium concentration. The corrosion rates of Fe-Cr alloys in ferric sulfate decrease with increasing concentration of chromium in the alloy. These observations are supported by the data on corrosion potentials of stainless steels in boiling acids and chlorides measured against a saturated calomel electrode. 

In order to evaluate the utility of the removal model for additional metals, additional removal studies were conducted using Chromium and Cobalt in place of copper. Chromium removal was studied using solutions made by dissolving CrO, in dilute H2SO4 to produce solutions with chromium concentrations of 80 ppm. The oxidation state of the chromium in the resulting solutions was not determined. Intraparticle diffusivities of Cr, Co", and Cu were calculated with the removal model, and are compared in Figure 7. The removal model for Dowex XFS 4195.02 appears to be generally applicable to most metals. 

A nice experiment illustrating the importance of a sample s matrix. The effect on the absorbance of copper for solutions with different %v/v ethanol, and the effect on the absorbance of chromium for solutions with different concentrations of added surfactants are evaluated. 

Tannins occur in many plants and are separated by extraction. At present, only quebracho extract is used as a mud thinner in significant quantity in the United States. Quebracho is an acidic material and performs best at high pH. It is an excellent thinner for lime-treated and cement-contaminated muds. However, it is not effective at high salt concentrations. Sulfomethylated tannin products are functional over a wide range of pH and salinity and have either been treated with chromium for good thermal stabiUty (58) or are chrome free. Concentrations of tannin additives are ca 1.5—18 kg/m (0.5—6 lb/bbl). 

By monitoring the intensity of the carbonyl absorption it was observed that oxidation of methyl 4,6-0-benzylidene-2-deoxy-a-D-Zt/ ro-hexopyrano-side with chromium trioxide-pyridine at room temperature gave initially the hexopyranosid-3-ulose (2) in low concentration, but attempts to increase this yield resulted in elimination of methanol to give compound 3. However, when methyl 4,6-0-benzylidene-2-deoxy-a-D-Zt/ ro-hexo-pyranoside is oxidized by ruthenium tetroxide in either carbon tetrachloride or methylene dichloride it affords compound 2 without concomitant elimination. When compound 2 was heated for 30 minutes in pyridine which was 0.1 M in either perchloric acid or hydrochloric acid it afforded compound 3, but in pyridine alone it was recoverable unchanged (2). Another example of this type of elimination, leading to the introduction of unsaturation into a glycopyranoid ring, was observed... 

Two ions of the transition metal take part in this reaction. However, in the case of supported one-component catalysts the formation of the active bond seems to occur on the interaction of the monomer with isolated ions of the transition metal. That may be illustrated by the data showing that the activity of chromium oxide catalysts decreases linearly with decreasing chromium content (or even increases per chromium ion) to the rather low (0.01%) chromium concentrations on the catalyst surface (62, 69). In... 

Alternatively, hexavalent chromium can be reduced, precipitated, and floated by ferrous sulfide. By applying ferrous sulfide as a flotation aid to a plating waste with an initial hexavalent chromium concentration of 130 mg/L and total chromium concentration of 155 mg/L, an effluent quality of less than 0.05 mg/L of either chromium species can be achieved if a flotation-filtration wastewater treatment system is used.15... 

Free, ionic species of metals are at their highest concentrations at lower pH, so metals tend to be more bioavailable under these conditions.121128 At acidic pH, more protons are available to saturate metal-binding sites.99 For example, metals are less likely to form insoluble precipitates with phosphates when the pH of the system is lowered because much of the phosphate has been protonated. Under basic conditions, metal ions can replace protons to form other species, such as hydroxo-metal complexes. Some of the hydroxo-metal complexes are soluble, such as those formed with cadmium, nickel, and zinc, whereas those formed with chromium and iron are insoluble. 

Results reported by various workers for chromium concentrations in seawater are listed in Table 2.1. In most of these methods, co-precipitation with... 

Mullins [37] has described a procedure for determining the concentrations of dissolved chromium species in seawater. Chromium (III) and chromium (VI) separated by co-precipitation with hydrated iron (III) oxide and total chromium are determined separately by conversion to chromium (VI), extraction with ammonium pyrrolidine diethyl dithiocarbamate into methyl isobutyl ketone, and determination by AAS. The detection limit is 40 ng/1 chromium. The dissolved chromium not amenable to separation and direct extraction is calculated by difference. In waters investigated, total concentrations were relatively high (1-5 xg/l), with chromium (VI) the predominant species in all areas sampled with one exception, where organically bound chromium was the major species. 

Dubovenko et al. [180] used chemiluminescence to determine total chromium in brines. The method is based on the enhancement of the chemiluminescence by chromium in the reaction of 4-(diethylamino) phthalhydrazide with hydrogen peroxide. The detection limit is 0.025 pg/1 of chromium, and the chemiluminescence is directly proportional to chromium concentrations in the range 5 x 10 10 to 10 6 M. 

Representatives of this phylum have been used extensively as indicators of stressed environments. Population structure and species diversity of free-living nematodes inhabiting sediments in the New York Bight were moderately influenced by the heavy-metal content of sands. In medium-grained sands, species diversity was inversely correlated with increased concentrations of chromium and other metals. Sands containing 3.0 to 21.5 mg Cr/kg were also marked by high relative abundances of one or two nematode species the tolerance of these species to chromium stress probably exceeded that of the normal nematode inhabitants of such sediments (Tietjen 1980). 

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