Papers by Keyword: Trivalent Chromium

Abstract: The tannery industry generally produces trivalent chromium waste (Cr3 +) and hexavalent chromium (Cr6 +). This waste before being released into the environment must meet quality standards according to KEPMENLH no.51 / MENLH / 10/1995 concerning liquid quality standards for industrial activities which says the maximum total chromium content is 0.6 ppm. This study aims to reduce the levels of Chromium in waste produced by the leather tanning industry by using alum coagulants. This research uses simulation waste which is made based on the results of BPPT analysis of waste in the leather tanning industry in Tangerang city, namely CV "Lengtat Tangerang Leather". The method used in this research is coagulation-flocculation with alum as a coagulant and lime as an alum reaction assistant in the form of hydroxide ions. The parameters observed in this study were the pH adjustment and the ratio of alum mass to lime mass. From the results of the study it was found that the decrease in the best chromium content for Cr + 3 occurred at a ratio of 5 and pH 8.2 which resulted in a chromium content of 0.0076 ppm with a decrease in percentage of 99.95%. As for the Cr6 + test, at a ratio of 3 and pH 6.4 the chromium content showed a value of 0.4110 ppm. The lowest chromium level occurs at a ratio of 5 and pH of 5.8 which results in a chromium level of 0.3341 ppm with a decrease percentage of 56.61%.

Abstract: The toxic metals released into the aquatic environment though various industrial processes are detrimental to all living species. This paper used banana peels as an adsorbent for studying heavy metal Cr(III) containing in waste water. Respectively, the effects of the adsorption dosage, temperature, contact time, pH, initial Cr(III) ions concentration and shock time on adsorption were investigated. The results showed that under the following condition: the dosage was 0.1 g, the pH value of the wastewater was 2, the temperature is 30 °C, the shock time was 2 h, the initial mass concentration of Cr(III) was about 30 mg/L, the adsorbing capacity can be 22 mg/g. The adsorption reaction is an endothermic process and mainly physical adsorption. Using banana peels to treat chromium-contained wastewater has a very good application prospect.

Abstract: The electroplated Ni-Co-Cr coatings were prepared on surface of a low carbon steel. The microstructure of the deposits were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD), the corrosion resistance of the deposits was evaluated using neutral salt-spray test and polarization measurement. The results show that the deposits are a Co and Cr solid solution in Ni with a grain size of 6.9~10.6nm, were nearly free of corrosion after neutral salt-spray tested 100 hours. With chromium content increasing, the coatings exhibited higher corrosion potential and lower corrosion current, which revealed excellent corrosion resistance.

Abstract: Gas quenching steel slag (GQSS) without any post treatment and modification could be utilized to remove Cr(III) from wastewater. Due to lower content of reductive material in GQSS, it was suggested that dissolved oxygen in solution should be declined slightly to the minimum with libration time, and then increased as the testing centrifuge tubes without lids because of dissolution of oxygen from atmosphere. Dissolved oxygen chromium original have significant influence on redox potential in solution. pH increased with the increasing of libration time because of dissolution of alkaline material in GQSS. But dissolution oxygen has little influence on pH in solution. It was suggested that Cr(III) removal percentage when the solution was sealed from atmosphere was slightly higher than that as the soltuion without seal, which was related with the influence of dissolved oxygen on pH and redox potential in solution.

Abstract: This study investigated the resistance of Deinococcus radiodurans to Cr6+ and Cr3+, the redox activity of this bacterium for Cr6+ and Cr3+ and the contributions of various bacterial components to the observed chromium resistance. The results showed that at 0.2 and 0.5 mmol/L of Cr6+, D. radiodurans displayed high growth with an early logarithmic phase. This organism also exhibited moderate growth at 2 mmol/L Cr3+. This strain exhibited strong reduction activity against Cr6+. At 0.2 mmol/L Cr6+, the 8-hour Cr6+ clearance rate was 92.13%. However, the clearance rate decreased sharply with increasing concentrations of Cr6+. At 0.5 mmol/L Cr6+, the 24-hour clearance rate was only 32.81%. By studying the effects of the cellular environment and individual bacterial components on the level of Cr6+, we discovered that D. radiodurans counteracted the effects of Cr6+ primarily through reduction and secondarily through adsorption. The primary activity was found to occur in the extracellular space and the cell culture supernatant. D. radiodurans had no significant oxidation effects on Cr3+. In conclusion, this study showed that D. radiodurans strongly reduces and is highly tolerant of Cr6+ and that the primary reducing agent is secreted from the cell.

Abstract: A black trivalent chromium conversion coating (CCC) was obtained on Zn deposit in chromium trichloride solution at 55 °C. The formation process of trivalent CCC on Zn deposit were thoroughly investigated by using X-ray fluorescence spectrometer and X-ray photoelectron spectroscopy in combination with atomic force microscopy surface analysis. The trivalent CCC on Zn deposit is consisted of Zn, Cr, O, Ni, Co, P and N elements, with visible micro-cracks on the film’s surface. The growth rate, the surface color and the morphology of this conversion coating vary with the dipping time.

Abstract: Cr-α-Al₂O₃ composite coatings were prepared by direct current deposition experiments from Cr(Ⅲ) plating bath and the thickness of composite coatings could be up to 14 μm. The obtained Cr-α-Al₂O₃ coatings and Cr coatings were characterized by means of EDS, SEM and microhardness measurement. Results revealed that Cr-α-Al₂O₃ coatings exhibit fine-grained structure with uniform surface and the highest microhardness values(692 HV) when the α-Al₂O₃ content of coatings was 15g/L, although some pores and defects are still present in the coatings. Analysis of Tafel curves indicated that the presence of α-Al₂O₃ in the Cr coatings show better features in the corrosion resistance both in H₂SO₄ and NaOH solution than those prepared from the bath without α-Al₂O₃.

Abstract: Gas quenching steel slag (GQSS), which was prepared by gas quenching equipment under inert atmosphere, possessed some advantages for pollutants removal from wastewater. Static state experiment has been carried on to investigate Cr(III) removal from wastewater by GQSS. The results indicated that solid-liquid ratio, Cr(VI) original concentration, libration time and dissolved oxygen have significant influence on Cr(III) removal percentage. Take economic cost into account, the ratio between the mass of GQSS and the volume of Cr(III)-bearing solution should be controlled at 3:100. Because Cr(III) removal from wastewater by GQSS went through absorption and precipitation, the removal percentage of Cr(III) increased gradually with the reaction time. Moreover, Cr(III) removal percentage declined with the increasing of Cr(III) original concentration. Along with the declining of dissolved oxygen under sealed with lid, the redox potential in the solution decreased, and then the removal percentage of Cr(III) increased.

Abstract: New Cr-Ni-ZrO₂ composite coatings are prepared by composite electrodeposition. The morphology, composition and corrosion resistance of as-deposited Cr-Ni-ZrO₂ coatings are systematically characterized by means of SEM, EDS. The hardness of as deposited and annealed Cr-Ni-ZrO₂ coatings are also discussed. The electrochemical corrosion tests are conducted by means of Tafel plots. Results of SEM and EDS show that Cr-Ni-ZrO₂ composite coatings with homogeneous and crack-free morphology have been prepared successfully; the mass proportion of Zr in the as-deposited coatings is up to 7.85%. The hardness values of Cr-Ni-ZrO₂ coatings are higher than that of Cr-Ni alloy coatings. Furthermore, the hardness values increase and then decrease with the temperature increasing when annealed. Analysis of Tafel plots demonstrates that Cr-Ni-ZrO₂ coatings have much better corrosion resistance than that of Cr-Ni coatings.

Abstract: Cr-Fe-ZrO₂ composite coatings were electrodeposited in trivalent chromium chloride electrolyte containing glycine as complexing agent. The effects of electrodeposition parameters such as current density and electroplating time on appearance, surface morphology and composition of the Cr-Fe-ZrO₂ composite coatings were investigated mainly. The obtained Cr-Fe-ZrO₂ composite coatings were characterized by means of scanning electron microscope (SEM) and energy disperse spectroscopy (EDS) techniques; the appearance quality was evaluated by range estimation; and the bonding force was analyzed by bending tests. The SEM results showed that the nano-size ZrO₂ powder were fairly distributed through out in the composite coating, and the composite coating contained only few fine cracks. The EDS results indicated that the composite coating contained chromium, iron, zirconium, oxygen, carbon and chlorine. The deposited coating was glossy and the results of bending tests showed that the bonding between the composite coating and the substrate was good