Separation by hydrazine extraction

Tantalum Niobium extraction separation (separation of niobium and tantalum by solvent extraction) to extract a single high-purity niobium compound from the niobium-tantalum emulated leather with a solvent, the intermediate product of the process of tantalum. This is a method of separation of cesium that is commonly used worldwide. Extraction System An extraction system consists of an aqueous phase and an organic phase. The aqueous phase of the extraction and separation of lanthanum and cerium is mainly composed of a hydrazine-containing aqueous solution of a hydrofluoric acid solution, an aqueous phase of a sulfuric acid solution, and an aqueous phase of an oxalic acid solution. Tantalum and niobium have sufficient solubility only in hydrofluoric acid. For example, when [HF]=418g/L, the solution contains Nb2O5775g/L; when [HF]=302g/L, the solution contains Ta2O51282g/L. In the hydrofluoric acid solution, ruthenium mainly exists as H2NbOF5, HNbF6, H2NbF7, and ruthenium mainly exists in the form of coordinated ions such as H2TaOF5, HTaF6, H2TaF5. Properties stronger than gold tantalum, niobium generate more stable H2TaF7, niobium easy to generate H2NbOF5 aspect, this difference is the basis for separation of tantalum and niobium. When using fluorohydrogen to decompose strontium concentrate, the addition of sulphuric acid can increase the decomposition rate of concentrate and increase the extraction rate and separation efficiency of hydrazine. Therefore, HF+H2SO4 mixed acid aqueous phase liquid is commonly used in industry. In addition to ruthenium in the aqueous phase liquid, there are also complexes such as impurities H2Ti0F4, H2TiF6, H2SiF6, Ti(S04)2. The solvent-extracted organic phase usually consists of a leather remover and a diluent. Nb - Ta separated industrially commonly used extraction agent methyl isobutyl ketone (of MIBK), tributyl phosphate (TBP), cyclohexanone, acetamide (full name mixing two N-N-alkyl acetamide), Secondary octanol. These extractants have their own advantages and disadvantages. For example, MIBK has good extraction selectivity, large extraction capacity for ruthenium, light density, low viscosity, stable operation, easy control, and can be extracted by pure water. It is widely used internationally. Extracting agent. It has high water solubility (up to 18.2g/t at 298K), low flash point (296.7K), and high volatility, which is a disadvantage. Secondary octanol and acetamide are extractants developed and used in China. The former has good extraction selectivity, low water solubility (0.08%), low price, but high viscosity, and emulsification is easy to occur during back extraction. The latter is suitable for the treatment of high turns ratios (Nb2O5: Ta2O5=7), high titanium (TiO2%), high tungsten (>10%) and decomposition products of phosphorus-containing antimony concentrate. The extraction selectivity of TBP is good, and the extractant is used by Cia Brasiloira de me tallurgia e Mineracao, the world's largest cesium extraction plant. Extraction mechanism In the HF-H2SO4 mixed acid aqueous phase solution, the extraction of lanthanum and cerium is an ionic complex extraction. For example, when TBP is extracted, the products are HTaF6•xTBP and HNbF6•xTBP (x=1~4). When the octanol extract is extracted, three kinds of extracts are formed, mainly the reaction of pure octanol (ROH) to extract ruthenium and osmium:

Where Me represents Nb or Ta. The industrially used octanol is actually a mixture of octanol and ketone (containing 10% to 15% of ketone), and there is a synergistic extraction reaction when extracting and separating ruthenium and osmium:

The extraction process is based on the ratio of ruthenium content in the raw materials, and is separately extracted or separated by co-extraction and back-separated. When the content of lanthanum and cerium varies greatly, most of them are extracted separately. Figure 1 shows the MIBK extraction of enthalpy and enthalpy curves. It can be seen from the figure that when extracting separately, the hydrazine is extracted first under low acidity, and then the hydrazine is extracted under high acidity. Co-extraction is the simultaneous extraction of hydrazine into the organic phase, and back-extraction of hydrazine and hydrazine from the supported organic phase of hydrazine, ie high acidity back extraction hydrazine, low acidity back extraction hydrazine. The common extraction method is simple and easy to operate, and is widely used in international factories. After the extraction of the organic phase into the organic phase, washing the loaded organic phase and back-extracting the separated ruthenium becomes a key link. Suitable detergents and stripping agents should be selected depending on the extractant and aqueous phase liquid used. For example, the secondary octanol-HF-H2SO4 extraction system usually washes the supported organic phase with a sulfuric acid solution, using H2SO41 mol/L.

The solution was back extracted with hydrazine and the hydrazine was back extracted with pure water. Increasing the volume ratio of the organic phase and the aqueous phase liquid solution can increase the extraction rate of the ruthenium, and the multi-stage extraction can completely extract the ruthenium. Other metal ions extracted in the form of fluorine complex in the aqueous phase liquid are Sn2+, Sn4+, RE3+, etc., and partially extractable are As3+, As5+, Mo5+, Se4+, Fe3+, W6+, V3+, V5+, Sb5+ and the like. The acidity of the aqueous phase is selected so that the saturated concentration of lanthanum in the organic phase is optimal, and the impurities extracted into the organic phase can be minimized. The impurities entering the organic phase are washed away with a sulfuric acid solution or a mixture of sulfuric acid and ammonium sulfate. It is best to wash the saturated octanol with H2SO44mol/L solution. The extraction equipment used in the extraction equipment industry for the separation of bismuth is a multi-stage tank type mixing clarifier or extraction tower (packed tower, sieve tray tower, etc.). Due to the high corrosive nature of the HF-H2SO4 mixed acid solution, a multi-stage box type mixing clarifier made of low-pressure polyethylene sheet, polypropylene sheet welded or lined with polytetrafluoroethylene material is generally used. After the slurry extraction of the cerium concentrate is leached by HF-H2SO4, the residual solid matter is less, and the solid residue is not separated by filtration, and is directly extracted as an extract liquid, which is called slurry leather extraction. China's pulp extraction method is widely used in China. Compared with the clear liquid extraction, the slurry extraction can eliminate the filtration and washing of the decomposition residue, shorten the production cycle, reduce the labor intensity, improve the working conditions, and facilitate the sealing and continuous process. In addition, the auxiliary equipment for filtration can be reduced, and the production capacity of the decomposition tank and the recovery rate of the crucible can be improved. When the supernatant is extracted, the residual lanthanum and lanthanum [(Ta+Nb)2O5] is 1% to 5% due to the leachate contained in the filtration residue; the residual liquid extracted from the slurry contains only (Ta+Nb)2O50.1g/L, There are very few defects lost in the slag. Slurry extraction is suitable for both raw materials with large changes in the content of niobium and for decomposition products of low-grade antimony concentrate. The bottom of the clarification chamber of the tank type mixing clarifier for slurry extraction has a slurry sedimentation zone, which is often impacted by the mixed phase discharge, so that the residue is not easily deposited in the extractor. The bottom of the clarification chamber is inclined to the mixing chamber by about 15. Eli residue flows to the mixing chamber. The extraction process of octanol slurry is shown in Figure 2.

It is expected that the effect of extraction and separation of the aqueous solution of hydrazine-containing hydrofluoric acid is good, the process is becoming more and more mature, and it will be widely used in industry. However, the problem of contamination of the aqueous phase liquid is serious and it is not easy to completely cure. To this end, it is necessary to develop other aqueous phase liquids that are safe and do not pollute or pollute the environment, such as aqueous sulfuric acid liquid, oxalic acid aqueous liquid, and the development of new high-efficiency extractants.

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