Showing papers on "Sodium dichromate published in 2017"

Current efficiency of individual electrodes in the sodium chlorate process: a pilot plant study

Abstract: Current efficiency in the sodium chlorate process is a key issue in the evaluation of the power consumption. A pilot cell unit for executing the sodium chlorate process was constructed to study the current efficiency of the anode and cathode separately. The effects of sodium dichromate and sodium sulphate concentrations and the electrolyte temperature on the anode and cathode current efficiencies were studied. Corrosion products formed on the mild steel cathodes after their removal from the cell were characterised using X-ray diffraction and infrared spectroscopy. The results show that the cathodic current efficiency increases with increasing dichromate concentrations in the electrolyte until approximately 5 g dm−3 is reached. At this optimum concentration of dichromate, the presence of sulphate ions decreases the cathodic current efficiency. For moderate increases in temperature, the cathodic current efficiency increases, but oxygen evolution is promoted, and the power consumption also increases. Surface characterisation of the electrodes after their exposure to air shows two primary types of behaviour, depending on the process parameters. At low dichromate concentrations, amorphous corrosion layers are formed, while at higher concentrations, reduced forms of iron hydroxides, i.e., “green rust”, are identified. Although the electrodes were positioned at the open circuit potential for 40 min before their removal from the cell, chromium remains on the cathode surface. This result might explain the corrosion-inhibiting effect of the addition of chromate to the electrolyte. The results from this study can be used to optimise operating procedures in real plants, decrease the energy consumption and minimise the environmental impact of these processes.

Method for preparing sodium dichromate through ultrasonic-microwave combination

Abstract: The invention relates to a method for preparing sodium dichromate through ultrasonic-microwave combination and belongs to the technical field of chromium salt production. The method comprises steps as follows: firstly, chrome iron ore is crushed and ground until particle size is 200 meshes or lower, sodium carbonate is added and mixed with obtained powder uniformly, under the microwave power being 1500 W, a mixture is subjected to microwave heating to reach 400-450 DEG C, the temperature is kept for 30-60 min, and the mixture is naturally cooled to the room temperature after constant-temperature treatment and is ground into a powdery material; distilled water is added to the powdery material, a mixture is subjected to leaching under the ultrasonic condition and subjected to suction filtration after leaching, and a ferric oxide solid impurity and a leachate are separated out; dilute H2SO4 is added to the obtained leachate until pH is 7-8, filtration and separation are performed again to remove an aluminium hydroxide solid impurity, dilute H2SO4 is added to a leachate obtained through refiltering until pH is lower than 5, a mixed solution is evaporated, concentrated, cooled and filtered, a product is washed and dried, and sodium dichromate can be obtained. The invention aims to reduce reaction temperature, increase conversion rate of chromium and reduce technological process.

Method and system for the integral chlorine dioxide production with relatively independent sodium chlorate electrolytic production and chlorine dioxide production

Abstract: A system for the integral chlorine dioxide production with relatively independent sodium chlorate electrolytic production and chlorine dioxide production is provided. The system may feed electrolyte solution into a solid-liquid filter, filtering out the crystal and eliminating sodium chloride and sodium dichromate. The sodium chlorate crystal may be fed into a chlorine dioxide generator after dissolving, while sodium chloride and sodium dichromate solution separately return to electrolyzer for electrolysis process. Sodium chloride may be constantly formed as a by-product in the chlorine dioxide production unit, and solution containing the sodium chloride is withdrawn from the generator and, after filtration, washing and dissolution, recycled back to sodium chlorate production unit. This way, there is no need of sodium chloride make-up.

Method for preparing anhydrous sodium chromate

Abstract: The present invention discloses a method for preparing anhydrous sodium chromate. The method comprises the steps of mixing a sodium chromate alkali solution with a carbonating solution in proportion of (1:1) to (8:1), and then, adjusting the pH to 6.5-8.5 to obtain a pretreatment solution of sodium chromate; placing the pretreatment solution of sodium chromate in an evaporation crystallizer for vacuum evaporation at the temperature of 80 DEG C to 120 DEG C under the pressure of 0.01 MPa to 0.09 MPa; and when the solid-to-liquid ratio reaches 10%-50% through vacuum evaporation, performing solid-liquid separation at the temperature of 70 DEG C or above to obtain anhydrous sodium chromate and a filtrate. Based on the technology characteristics of sodium dichromate preparation by a carbonation method, high-quality anhydrous sodium chromate is successfully prepared by the method disclosed by the invention, with the main content being equal to or greater than 99.5% and the content of all impurities such as sulfate being less than 0.001%; moreover, the product does not absorb moisture or cake even if stored for a long term, and has good fluidity. The problems of sodium chromate tetrahydrate on easy moisture absorption, caking and poor fluidity are successfully solved. The method also brings into play the superiority of a production process of preparing sodium dichromate from a chromium salt by the carbonation method, so that two high-quality chemical products can be produced on one production line.

Method for desulfurizing flue gas by evaporated condensed water containing hexavalent chromium

Abstract: The invention discloses a method for desulfurizing flue gas by evaporated condensed water containing hexavalent chromium, according to the mechanism that redox reaction of sodium dichromate and sulfur dioxide is easy to occur, by direct use of the evaporated condensed water containing the hexavalent chromium, the purpose of desulfurizing of the flue gas is realized, a traditional alkali desulfurization process is replaced, waste is treated by the waste, cost is saved, environmental protection wastewater discharge pressure is reduced, and ultimately a chromium oxide green product with the content of more than 94% is produced.

Preparation method of passivant for automobile powdered metal part

Abstract: The invention discloses a preparation method of a passivant for an automobile powdered metal part. The preparation method comprises the step that water, sodium dichromate, glycidol, ludox, para toluic acid, sodium hydroxide, light calcium carbonate, an acrylic emulsion, magnesium oxide, cellulose nitrate, polyvinyl alcohol, potassium phosphate, sodium carbonate, 2-methylimidazole and dibutyl phthalate are weighed. The preparation method is simple, low in cost, high in operability, free of pollution to the environment, safe, environmentally friendly, resistant to acid and alkali and excellent in moisture resistance; a product with a film formed is high in strength, the adhesive force is 1 level, the corrosion resistance is good, heat shock resistance is achieved, the impact strength is 60-100 J, the viscosity is 65-85 s, and the adhesiveness is 250-290; the process stability is good, the service life is long, no remarkable change occurs after 6-10 years after the film is formed, using is easy, the film is firm and resistant to abrasion, the glossiness is good, the 60-degree glossiness is 92-98%, and the flexibility is 1 mm; and a finished product is atoxic, the hardness is 5-9, no wastewater is discharged, and sources of raw materials are extensive.

Vehicle exhaust pipe

Abstract: The invention discloses a vehicle exhaust pipe. The vehicle exhaust pipe is produced by the following raw materials: steel products, aluminum products, copper products, linear alkyl benzene sulfonate, octaphenyl polyoxyethyiene, glycol, phosphoric acid, sodium dichromate, zinc oxide, micron graphite fibers, and micron potassium feldspar. The linear alkyl benzene sulfonate, the octaphenyl polyoxyethyiene, the glycol, the phosphoric acid, the sodium dichromate, the graphite fibers and the potassium feldspar are added on the basis of traditional materials of the vehicle exhaust pipe for improvement to improve the rust resistance, wherein the linear alkyl benzene sulfonate, the octaphenyl polyoxyethyiene, the glycol, the phosphoric acid, the sodium dichromate and the potassium feldspar not only can effectively promote a permeation effect between the raw materials and the steel products, the aluminum products and the copper products, but also can form a layer of protective film on a product to achieve a rust resisting effect; and in particular, the potassium feldspar can effectively promote mutual permeation among all the raw materials to reduce the gap of the vehicle exhaust pipe so as to further improve the rust resistance.