Sodium chlorate

About: Sodium chlorate is a research topic. Over the lifetime, 791 publications have been published within this topic receiving 6844 citations.

Energy efficiency in the sodium chlorate process: From electrocatalysis to pilot plant investigations

Abstract: Sodium chlorate is an important industrial chemical produced through an electrochemical manufacturing process. The global production rate is 3.6 million tons annually and consumes approximately 20 TWh of electrical power. The majority of the produced sodium chlorate is used as raw material to make chlorine dioxide for the bleaching of kraft pulp. This thesis aims to provide a deeper understanding on the mild steel cathode and the role sodium dichromate has in the electrolyte in the chlorate process. Such understanding would allow reduction of the energy consumption, in particular, as well as the overall manufacturing footprint. Two separate sodium chlorate plants have shown different performances in terms of current efficiency and corrosion of the mild steel cathodes. Surface characterisations and current efficiency measurements were performed on the two cathodes in order to evaluate the difference in performance between the samples. Two types of FeOOH were found on the individual cathodes: goethite (α-FeOOH) on the normally performing cathode and lepidocrocite (γ-FeOOH) on the poorly performing cathode. The two different FeOOH species were synthesised in pure form to elucidate if their electrocatalytic properties were the reason for their different performance. Both goethite and lepidocrocite showed lower activity for the reduction of water compared to polished mild steel but almost equally good towards hypochlorite reduction. The difference in performance of the pure phases can therefore not explain their differences in behaviour in large scale performance. However, in situ Raman spectroscopy revealed that the active species on the surface of the mild steel cathode was Fe(OH)2 and the kinetics for the reduction of the surface from Fe(III) to Fe(II) was also found to be different between the two types of corrosion products. These findings are the reason for the observed differences in current efficiency. Reduction of hypochlorite is the most important loss reaction in the chlorate process and Cr(VI) is added to the electrolyte to inhibit this reaction. A Cr(III) film formed at the cathode provide selectivity towards hydrogen evolution. The mechanism of hypochlorite reduction at Fe(III) and Cr(III) was studied by Density Functional Theory (DFT) calculations in order to understand the blocking effect of the Cr(III) film. The electro catalytic properties was shown to be very similar for Fe(III) and Cr(III) and cannot explain the blocking effect of Cr(III). However, the experimental results clearly demonstrated that the Cr(III) film was completely blocking of the hypochlorite reduction. It was concluded that it is the semiconductor properties of the materials that explain that the hypochlorite reduction at Cr(III) is inhibited while the reduction readily can proceed at iron (oxy)hydroxides. A pilot plant was used to investigate the long term effects from continuous operation. Three process parameters were tested in the pilot plant to investigate the formation of different corrosion products on the cathode surface and their effect on the energy efficiency. These three were concentration of dichromate, sulphate and the temperature of the electrolyte. The pilot plant studies revealed possibilities to optimise the current efficiencies and corrosion of the cathodes with respect to the operating and shutdown conditions. Finally recommendations are issued, as to how a sodium chlorate producer should relate to the results in order to minimize the losses in current efficiencies and cathodic corrosion.

Hydrometallurgical Pretreatment Process for the Recovery of Valuable Metals from the Lead Anode Slime

Abstract: After stacking pre-oxidation treatment, lead anode slime was leached in sulfuric acid added with sodium chloride and oxidant of sodium chlorate. The leaching rates of As, Te, Sb, Bi and Cu are more than 98% with potential controlled at 500mV. And noble metals are left in the residue, which are separated from the base metals effectively. Through cooling and crystallizing out arsenate, the solution is reduced with potential controlled. According to reducing slag, the recovery rate of Te is 96.52%. Sb is recovered by neutralizing hydrolysis and the recovery rate is 95.2%. By the effect of iron powder, As, Bi and Cu are entirely reduced with the recovery rates of Bi and Cu to be 91.56% and 83.49%, respectively. The total recovery of As from the crystalline product and reducing slag achieves 91.56%.

Method for producing high purity chlorine dioxide food additives

Abstract: The production method of high-purity chlorinedioxide food additive belongs to a method for producing chlorinedioxide disinfectant preservative and fresh-keeping agent which can be used as additive for food, and mainly is characterized by that it uses sodium chlorate, oxalic acid and sulfuric acid as raw materials to produce chlorinedioxide gas, then said gas is cleaned by using 5-15% urea solution, and then absorbed by alkaline stabilizing agent so as to obtain the high-purity, high-concentration and high-stability stabilized chlorinedioxide solution. The composition of said stabilizing agentconsists of sodium carbonate, hydrogen peroxide, sodium dodecasulfonic benzoate and 8-quinolinol according to the weight ratio of 1 : 0.2-0.9 : 0.002-0.01 : 0.0002-0.001.

System for controlling cupric chloride-sodium chlorate etching solution

Abstract: PROBLEM TO BE SOLVED: To provide a practical method for controlling a cupric chloride-sodium chlorate etching solution. SOLUTION: The cuprous chloride generated in copper etching by a cupric chloride-sodium chlorate etching solution is regenerated according to the equation: 6CuCl+NaClO3+6HCl→6CuCl2+NaCl+3H2O. In this case, the pH of the etching solution is set at 0.5 to 2.5, the ORP value at +500 to +1200 mV, the concentration of sodium chlorate at 0 to 1 mol and the specific gravity at 1.25 to 1.45 to control the solution. A sample measuring cell, a pH sensor, an ORP sensor, a specific gravity sensor and a temperature sensor are provided, and further, a device for processing the signal outputs from the respective sensors is furnished to perform this method.

Novel chlorine dioxide generator

Abstract: The utility model discloses a novel chlorine dioxide generator which comprises a reactor, a controller, a control panel, a hydrochloric acid stock tank, a sodium chlorate stock tank, a hydrochloric acid metering pump, a sodium chlorate metering pump and a water injector, wherein a hydrochloric acid feeding port, a sodium chlorate feeding port, a water inlet, a gas inlet, a chlorine dioxide outlet and a raffinate draining port are formed in the reactor; the hydrochloric acid stock tank is communicated with the hydrochloric acid feeding port through a hydrochloric acid feeding pipe; the sodium chlorate stock tank is communicated with the sodium chlorate feeding port through a sodium chlorate feeding pipe; the hydrochloric acid metering pump and the sodium chlorate metering pump are mounted on the hydrochloric acid feeding pipe and the sodium chlorate feeding pipe respectively; the chlorine dioxide outlet is connected with the water injector through a chlorine dioxide draining pipe; the water injector is further connected with a high water pressure pipe, a pressure gauge and a pressure regulating valve I are arranged on the high water pressure pipe, and a pressure regulating valve II is arranged on the chlorine dioxide draining pipe; and the hydrochloric acid metering pump, the sodium chlorate metering pump and the control panel are connected with the controller. The novel chlorine dioxide generator is simple in structure, practical and environment-friendly.