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SOURCES OF HYDROSULFITE IN PULP MILLS NaBH 4 + 8 NaOH + 8 SO 2 4 Na 2 S 2 O 4 + NaBO 2 + 6 H 2 O hydrosulfite borate Solid sodium hydrosulfite and hydrosulfite bleach solution containing pH buffer & other stabilizers can both be purchased Sodium hydrosulfite can also be produced on-site using the Borol Process
with kaolin deposits to a colorless form by the following reaction. +3 Na 2 S2042+ 6Fe+ + 4 H20 ---) 2 NaHS04 + 6Fe + 6H (Conley et al,1964) At present, sodium hydrosulfite is used by the kaolin industry as the reductive bleach. It is often purchased CCIIIIIIIBrCially as .
The reduction properties of Sodium Hydrosulphite also eliminate excess dye, residual oxide, and unintended pigments, thereby improving overall colour quality. Reaction with formaldehyde produces Rongalite, which is used as a bleach, in, for instance, paper pulp, cotton, wool, leather, chrome tanning agent and kaolin clay.
Sodium borohydride, used in combination with sodium bisulfite, is recognized by leading researchers as a replacement for sodium hydrosulfite in vat dyeing, indigo dyeing, color stripping, reductive clearing, machine cleaning and many other applications where a stable, environmentally desirable reducing agent is .
Reagents used to bleach or "brighten"high-yield pulps (high lignin content retained after bleaching) are milder in their action than reagents used for delignification. Both mild oxidative and reductive treatments are effective; the most commonly used reagents are hydrogen (sodium) peroxide and sodium dithionite (hydrosulfite).
dioxins. In fact, the most abundant dioxin produced by the pulp and bleaching process, 2,3,7,8-tetrachlorodibenzo- p -dioxin (2,3,7,8-TCDD), has been found to be both a carcinogen and a deadly toxin .Thus, chlorine as a bleaching agent is being replaced by the safer bleaching agents chlorine dioxide and hydrogen peroxide.
) and sodium hydroxide. Application Rohm and Haas offers a family of Sodium Borohydride-based brightening technologies for many bleaching applications. A BOROL Bleach generating unit allows a mechanical pulp mill to generate its own Sodium Hydrosulfite bleach on-site at substantially reduced cost relative to merchant Hydrosulfite bleach.
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Sodium hydrosulfite is the bleaching agent of choice for (chemi)mechanical pulps when a moderate (4-14 points) brightness increase is required [2]. Hydrogen peroxide is preferred for higher brightness gains, e.g., between 10 and 20 points [2].
Orthogonal Experiments for Kaolin Bleaching by Using Sodium Dithionite and Sulfuric Acid Article in Advanced Materials Research 968:116-124 · June 2014 with 97 Reads How we measure 'reads'
Aug 26, 2020· Sodium Dithionite (Hydrosulfite) Useful for iron stains only, wash extensively before and after, use a 2% concentration; can add a chelating agent like polyphosphate; addition of alkali like ammonia will slow down the procedure but will also decrease rate of decomposition of bleach; fumehood required when handling large volumes of solutions.
Most reductive bleaching of wool is carried out using stabilized dithionite (2–5g/L) at pH 5.5–6 and 45–65 C for 1 h. Thiourea dioxide is more expensive than sodium dithionite, but is an effective bleach when applied (1–3 g/L) at 80 C and pH 7 for 1 h.
Sodium hydrosulfite is used as a reducing agent in dying application. It undergoes reduction reaction with water-insoluble vat dye and sulfur dye to form water-soluble alkali metal salt of the dye (leuco form ) so that they have affinity for the textile fiber.
Residential without plant uptake. 200 .... The mechanism of Cr(VI) treatment using sodium dithionite (Na2S2O4) involves the conversion of... Get Quote; Sodium dithionite - ipcs inchem. Nov 14, 2002 ... processing of sodium dithionite and from the use of the substance itself, .... consumption of oxygen in biological sewage treatment plants or ...
Heavy metal ions have a harmful effect on bleaching. Treatment of the pulp with chelating agents has a favourable effect on bleaching efficiency (Melzer & Auhorn, 1981).Chelating agents are often premixed dry with the sodium dithionite by the supplier. Reducing dithionite has a higher kinetic reaction rate compared with hydrogen peroxide.
Sodium dithionite is a combustible solid which slowly decomposes when in contact with water or water vapor, forming thiosulfates and bisulfites. This reaction evolves heat, which can further accelerate the reaction or cause surrounding materials to burn.
Sodium hydrosulfite is also used as commercial bleach for treatment of leather, kaolin clay, fur and chrome tanning. Hazards Identification Hazard Warnings: Sodium Hydrosulphite may ignite with moisture and air. harmful if swallowed or inhaled. causes irritation to skin, eyes and respiratory tract.
In a process for treating raw kaolin clay to improve the color and brightness by treating the clay in an aqueous dispersion with sodium dithionite, the improvement consisting of treating the dispersion with hydroxylamine or salt thereof after the treatment with sodium dithionite is complete.
The reduction properties of sodium dithionite also eliminate excess dye, residual oxide, and unintended pigments, thereby improving overall color quality. Sodium Hydrosulphite can also be used as bleach in paper pulp, cotton, wool, and kaolin clay. Sodium Hydrosulphite is used for water treatment, gas purification, cleaning, and stripping.
Sodium dithionite may also be used as a bleach for leather. Paper industries use Sodium Hydrosulfite for bleaching of the wood pulp and producing white paper. In chemical industries, Sodium hydrosulfite (sodium dithionite, Na2S2O4) is an inexpensive and safe reducing agent, which for example enables the reduction of aromatic nitro and diazonium ...
Sodium hydrosulfite's reduction reaction removes residual oxide and wrong pigments. Sodium hydrosulfite is a reductive bleaching agent. It reduces carbonyl and alcohol groups, which function as colorants of the substances. It is used in bleaching mechanical paper pulp, cotton, wool and kaolin clay.
An alternative form of sodium dithionite is sodium sulfoxylate formaldehyde, which is prepared by the reaction of formaldehyde with the dithionite. Its applications are like those of dithionite, except that it is less reactive and more stable thermally. When the sulfoxylate is used, .
Improved methods for bleaching kaolin clay and other minerals are provided. More particularly, methods of the present invention employ a hydrosulfite or bisulfite material and a second reducing agent, preferably a reducing agent that contains a Group III element, such as a borohydride, to increase the brightness of kaolin clay and other minerals and reduce color present therein.
Anhydrous sodium dithionite decomposes to sodium sulfate and sulfur dioxide above 90 °C in the air. In absence of air, it decomposes quickly above 150 °C to sodium sulfite, sodium thiosulfate, sulfur dioxide and trace amount of sulfur. Redox reactions. Sodium dithionite is a reducing agent. At pH=7, the potential is -0.66 V vs NHE.
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