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Ammonia Condensation in Ammonium Paratungstate Crystallization Affecting Factors

Details: Category: Tungsten Information; Published on Thursday, 07 January 2016 20:20; Written by chunyan; Hits: 273

Condensation of ammonia tail gas from ammonium paratungstate is affected by many factors. Condensing often refers to the physical condensation process of the constant or high temperature gas, liquid cooled down, also reaction produced by polymerization of two or more physical. Studying the law NH3 saluted in water t different temperatures, and adopting appropriate technology and equipment will make a good effect on NH₃ recovery. We analyze from the following 3 factors:
1. Area ratio of condensation and evaporation (Short for S_c/S_e)
The concentration of ammonia decreased with the increasing of Sc/Se in APT crystallization. In the early evaporation stage, low temperature of the solution, high concentration of ammonia, much NH₃ escaped and small amount of evaporation lead to higher concentration of ammonia; in the latter stages, temperature rising lead to ammonia concentration reduced, and less NH₃ escaped, moisture evaporation, condensation of ammonia declining. When in the right Condensation strength, NH₃ absorbed in water at maximum; the smaller S_c/S_e is disadvantage to absorb ammonia gas; the larger S_c/S_e will increase the condensation amount, resulting in the decrease of the concentration of ammonia.
2. Evaporation temperature
The saturation water vapor will increased with the evaporation temperature increasing, and the more water condensation will dilute ammonia, so low temperature evaporation is conducive to improve the concentration of ammonia.
3. Stirring speed
Evaporation of H₂O and evaporation are the process of liquid→gas during the APT crystallization, and stirring can promote the concentration of ammonia.

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Sodium Tungstate -Hydrogen Peroxide System Catalyzing-Degrading Methylene Blue

Details: Category: Tungsten Information; Published on Thursday, 07 January 2016 19:55; Written by linlu; Hits: 258

Hydrogen peroxide is colorless transparent liquid and a strong oxidizer. But because it is not stable, the actual amount is greater than theoretical dosage. When it’s used alone, the degradation effect is often not ideal. Methylene blue is a kind of aromatic heterocyclic compounds. It’s soluble in water, ethanol and insoluble in ether. Aqueous solution is blue in the oxidizing environment, but in reducing agent of zinc, ammonia water it can be restored into a colorless form. Methylene blue is widely used in chemical indicator, hemp, silk fabric, paper, bamboo, wood dyeing and the shading. It can also be used in the manufacture of ink and dyeing of organisms, bacteria and organization. At the same time, the methylene blue also has oxidability and its degradation is more difficult.

Based on the difficult degradation of methylene blue solution as the simulated printing and dyeing wastewater, this article discussed sodium tungstate-hydrogen peroxide system catalytic oxidation and degradation of methylene blue. The experiment can be divided into the following steps:

1. Use deionized water to prepare 0.01 mol/L sodium tungstate solution and 10 mg/L of methylene blue simulated printing and dyeing wastewater respectively.

2. Take 100 ml methylene blue solution to a beaker, adding suitable amount of sodium tungstate solution. After sulfuric acid or sodium hydroxide solution adjusting the pH of the solution, slowly stir it in constant temperature magnetic stirrer.

3. When reaching the set temperature, add a certain amount of hydrogen peroxide solution. Start the time and take samples in interval time. Test its absorbance in 660 mm of methylene blue maximum absorption wavelength.

4. Water samples before and after treatment were taken photometry and ultraviolet visible from curve analysis of the degradation products.

5. Use Cu electrode as working electrode, Pt electrodes as auxiliary electrode, saturated calomel as reference electrode. Measure water samples before processing, hydrogen peroxide water samples and sodium tungstate - hydrogen peroxide water samples respectively.

The results showed that the degradation rate of methylene blue was near 100% after 40min of reaction in sodium tungstate-hydrogen peroxide system. The optimum conditions for 100mL methylene blue (10mg/L) degradation were as follows: reaction temperature 60℃, sodium tungstate(0.01mol/L) dosage7.0mL, 30% hydrogen peroxide solution dosage 3.5mL. The degradation of methylene blue was effective in a wide range of pH value 1~14. Sodium tungstate-hydrogen peroxide system has an obvious catalyzing and degrading effect of methylene blue simulating dyeing-wastewater.

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Sodium Tungstate and SLS Composite Corrosion Inhibition to Carbon Steel1/2

Details: Category: Tungsten Information; Published on Thursday, 07 January 2016 19:46; Written by linlu; Hits: 252

Water treatment agent is the generic terms of chemicals used in water treatment. It usually refers to chemicals used in wastewater treatment. It is widely used in petroleum, chemical industry, metallurgy, transportation, light industry, textile and other industrial sectors. Water treatment agent includes corrosion inhibitor, scale inhibitor, bactericide, flocculating agent, cleaning agent and so on. In practical application, people often use the compound formula of water treatment agent, or the integrated application of various types of water treatment agent. Therefore, we should not only pay attention to confrontation as a result of improper distribution between various components, but also make full use of synergies to increase efficiency.

Pipeline and equipment contacting with seawater chronically are subjected to corrosion damage. Accidents and great economic losses can be caused. So adding corrosion inhibitor is one of the important ways to control the corrosion. Cooling water corrosion inhibitors commonly used are chromate, nitrite and phosphate which are most toxic and not green. Sodium tungstate is a kind of avirulent and harmless inorganic corrosion inhibitors. Corrosion is more efficient after distribution with sodium lauroyl sarcosine (SLS). This article mainly introduces corrosion inhibition of sodium tungstate and SLS composite to carbon steel in simulated seawater. The experiment mainly adopts weight-loss method and electrochemical method.

Weightlessness method:

1. Burnish the lacing film light firstly. Swab it with alcohol and acetone. Weigh after cold wind blowing dry.

2. Hold right amount of simulate water in the big beaker equipped with a stirrer. After adding corrosion inhibitor, put it in 45 ℃ thermostat.

3. The lacing film will be prepared in suspension to corrosion medium. Start the blender to make the corrosive medium in the flow state.

4. Take out corrosion coupon after 48h, wrapped in filter paper. Put it in the dryer 12h to weigh. Measure the corrosion rate lastly.

Electrochemical method:

1. Use three electrode systems, including homemade Q235 steel electrodes as working electrode.

2. Working electrodes in metallographic pre grinding machine are burnished to a smooth surface step by step, and then clean with deionized water, alcohol and acetone in turn. Dry it with the cold wind.

3. Before the measurement, soak the working electrode in corrosion medium around 30 min to the corrosion potential. Then start testing from the corrosion potential. Finally calculate efficiency of the corrosion by Tafel polarization curve and ac impedance spectrum.

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Sodium Tungstate and SLS Composite Corrosion Inhibition to Carbon Steel 2/2

Details: Category: Tungsten Information; Published on Thursday, 07 January 2016 19:48; Written by linlu; Hits: 278

As is known to all, sodium tungstate as a new type of corrosion inhibitor is non-toxic，harmless and environmental friendly. To achieve better corrosion effect, the adding amount of sodium tungstate needs to be higher. In order to reduce the amount of sodium tungstate and better inhibit pitting corrosion at the same time, sodium tungstate should mix with other corrosion inhibitors to achieve synergies.

Sodium lauroyl sarcosine (SLS) is a new type of corrosion inhibitor developing in recent years. It’s white to pale yellow liquid and has a special odor. It’s soluble in water, ethanol, glycerol alcohol and aqueous solution. In normal conditions, it’s relatively stable to heat, acid and alkali. It has low toxicity, low irritation and is easily biodegradable. Cost is reasonable. In metal processing it is often used as a corrosion inhibitor, rust remover and so on.

Mentioned in the previous article, using weight loss method and electrochemical method can determine corrosion inhibition of sodium tungstate and SLS composite to carbon steel in simulated seawater. Through the experiment we can draw the following conclusions:

1. In the simulated seawater, sodium tungstate has the corrosion inhibition effect on carbon steel. Corrosion inhibition efficiency increases with the increase of its concentration. Sodium tungstate adsorption is the mixed adsorption on the surface of the carbon steel.

2. After adding SLS, the corrosion effect increases greatly. After adding 40 mg/L SLS and 600 mg/L sodium tungstate, corrosion inhibition efficiency increases from 62% to 84.4%. It shows both have synergy effect. Comparing corrosion lacing film situation, pitting corrosion decreases significantly after adding SLS. When the SLS adding amount is 60 mg/L, pitting corrosion phenomenon disappears.

3. One-component sodium tungstate inhibitor requires high concentration. After adding the composite corrosion inhibitor, polarization resistance becomes larger which shows that composite corrosion inhibition effect is more obvious. It has a synergistic effect. When the 600 mg/L sodium tungstate and 120 mg/L SLS compositing, corrosion inhibition efficiency is more than 95% and corrosion rate also drops below 0.075 mm/a. it belongs to mixed type inhibitor.

In a word, sodium tungstate and sodium lauroyl sarcosine composite is better than single use and has good synergistic corrosion inhibition effect. The composite corrosion inhibitor is mixed type corrosion inhibitor.

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Indirect Condensation Absorption Disposing Ammonia in Ammonium Paratungstate Crystallization

Details: Category: Tungsten Information; Published on Thursday, 07 January 2016 18:20; Written by chunyan; Hits: 250

Ammonium paratungstate (APT) crystallization is the process of the polymerization of ammonia and acid. Ammonia (NH₃) volatiles out from the solution the volatilized ammonia in the heating process. It will cause atmospheric pollution if ammonia discharged directly into the air. Ammonia combines with hemoglobin easily and destroys the function of oxygen transportation, even lead to death.

Ammonia, commonly known as NH₃, is a colorless and tasteless gas, with a strong pungent odor, easily soluble in water, 1 volume of water can be dissolved 700 times the volume of ammonia under normal temperature and pressure. The environment department of China stipulates that waste water of tungsten smelting is the first class of elements to discharge the waste gas, zero discharge requirements is demanded. So, it is necessary for enterprises to take a new and efficient way of recycling tail gas in APT crystallization, in order to achieve the goal of zero emissions of ammonia gas.
Ammonia tail gas recovery

Indirect condensation method is an effective method for recovery of ammonia from APT tail gas. Two ways to recover ammonia produced from ammonium paratungstate crystallization.
1. Condensed into ammonia and returned to the reaction process;
2. Converted into NH₄Cl and return to desorption of ion exchange process.
Compared the two ways, the front is of higher economic value. NH₃ and water are polar molecules, ammonia and water molecules combining and becoming a hydrogen bond when NH₃ soluble in water. With temperature increasing, the solubility of ammonia in water becoming lower, so the low-temperature condensation is an effective way to improve the recovery rate of ammonia.

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