[Background and Overview][1][2][3][4]
Oxalate is a salt formed from oxalic acid and contains oxalate ions (C2O42− or (COO)22−). Since oxalic acid is a dibasic acid, oxalates are divided into two types: ortho-salt oxalate and acid salt hydrogen oxalate, the latter containing HC2O4− . Oxalic acid and oxalate are anti-nutritional factors widely present in plant feeds. They can significantly reduce the utilization of mineral elements by animals, and can cause damage to many organs and cause poisoning. Ruminants are the main herbivores. Therefore, in actual production, oxalate is very harmful to ruminants, and oxalate poisoning often occurs.
Oxalate is a component that normally exists in plants. It can be divided into soluble oxalate and insoluble oxalate. The soluble oxalate mainly includes sodium oxalate, potassium oxalate and ammonium oxalate, and the insoluble oxalate mainly includes oxalic acid. Calcium, magnesium oxalate and iron oxalate. The main pathways for the formation of oxalate are glyoxylate oxidation under photorespiration, cleavage of vitamin C and isocitrate, and oxaloacetate hydrolysis. Among them, the glyoxylate oxidation pathway is considered to be the most direct and direct way for plants to accumulate oxalate. effective way. When ruminants ingest oxalate-containing plants, oxalate is metabolized in four forms.
First, oxalate will be degraded by rumen microorganisms;
Secondly, when the feed contains high calcium, oxalate will combine with calcium in the rumen or small intestine to form insoluble calcium oxalate crystals, which will be excreted through feces;
Third, when the calcium content in the feed is low, oxalate will be quickly absorbed by the intestines into the blood. When the concentration of oxalate ions in the blood is very high, it will form insoluble grass with the calcium and magnesium ions in the blood. The oxalate crystallizes, which in turn affects the formation of kidney urine and leads to renal failure; fourth, insoluble oxalate will pass directly through the intestines and will not affect the body's metabolism.
[Symptoms and mechanisms of oxalate poisoning][1]
Many animal experiments have shown that soluble oxalates can rapidly bind to calcium or magnesium in the serum, thereby abruptly lowering the concentrations of these ions. Acute oxalate poisoning can sharply reduce the calcium concentration in the serum, affect the animal's normal cell function, cause the animal's muscle tremors, circulatory collapse, and eventually death. In chronic oxalate poisoning, insoluble calcium oxalate can severely damage the renal tubules. Finally, even if the animals do not die from hypocalcemia and cellular energy metabolism disorders, they will die from renal failure. When cattle are poisoned by oxalate, they may suffer from loss of appetite, depression, unresponsiveness, constipation, dry mouth, prolonged blood coagulation time, reduced rumen motility, frequent standing and lying down, muscle weakness, abnormal gait, accelerated heart rate, muscle tremors and twitching; Frequent urge to urinate, and occasional discharge of brown-red urine; shortness of breath and difficulty, bloody foamy liquid flowing from the nose; eventually paralysis, lying on the ground, or even coma. When oxalate poisoning occurs, the body will show weakness, ataxia, twitching, and coma. Oxalates can affect energy metabolism and blood glucose levels.
[Preparation method][2]
At present, the main methods for preparing functional materials and their precursors using oxalate include: oxalate co-precipitation method, microemulsion reaction method, sol-gel method, etc.
1. Oxalate co-precipitation method
The basic principle of the oxalate co-precipitation method: The oxalate precipitation method usually mixes substances with different chemical compositions in a solution state, and adds the precipitant M2C2O4 (M stands for H+, NH+4, K+, Na+) is used to prepare a precursor precipitate, and then the precipitate is filtered and then dried or calcined to obtain corresponding powder particles. The particle size of the generated particles usually depends on the solubility of the precipitate. The smaller the solubility of the precipitate, the smaller the particle size. The particle size tends to increase as the supersaturation of the solution decreases. Characteristics of the oxalate co-precipitation method: Compared with some other traditional inorganic material preparation methods, the oxalate precipitation method has the following advantages: 1) The process and equipment are relatively simple, which is conducive to industrialization; 2) The content of each component can be controlled , to achieve uniform mixing between different components; 3) During the precipitation process, the precipitation conditions can be controlled, such as changing the concentration, temperature, pH value, stirring intensity and other experimental conditions of the oxalic acid and polynitrate mixed solution, as well as the next step of precipitation. The calcination temperature is used to control the purity, particle size, dispersion and phase composition of the obtained powder; 4) The sample calcination temperature is low, the performance is stable and the reproducibility is good. However, powder prepared by oxalate precipitation may form a severe agglomeration structure, thereby destroying the properties of the powder. It is generally believed that agglomerates may be formed during precipitation, drying and calcination processes. Therefore, in order to prepare uniform and ultra-fine powder, the entire process of powder preparation must be strictly controlled.
2.Microemulsion method
Microemulsions used to prepare ultrafine particles are often W/O type systems, often composed of four components: organic solvent, aqueous solution, active agent, and co-surfactant. Commonly used organic solvents are mostly C6-C8 linear hydrocarbons or cycloalkanes; surfactants generally include AOT [sodium bis(2-ethylhexyl)sulfosuccinate]. SDS (sodium dodecyl sulfate), SDBS (sodium cetyl sulfonate) anionic surfactant, CTAB (cetyl trimethyl�Related to purity, it is also closely related to particle morphology, particle size, and particle size distribution. Since high-definition color TV picture tubes adopt a point-shaped phosphor screen structure, the diameter of the phosphor dots is required to be very small. For this reason, phosphors with small particles with an average particle size of less than 2 μm and long afterglow and no flicker can meet the requirements. Y2O3: Eu3+ red phosphor is widely used in color TV picture tubes, three-primary color fluorescent lamps, projection TV picture tubes, and flying spot scanning wait. Mix Y2O3 and Eu2O3 in proportion and dissolve them in nitric acid, and prepare a separate oxalic acid solution Place it in a three-neck bottle, add a small amount of surfactant, keep the water bath temperature at a certain value, and then add nitric acid solution of Y and Eu. The resulting precipitate is washed, filtered, dried, and calcined to obtain uniformly distributed ultrafine Y2O3: Eu3+ powder. Compared with micron crystals, the emission spectrum of the nanocrystals has a significant blue shift, and the color coordinates meet the requirements of phosphors.
5. Preparation of superconducting materials
YBaCuO high-temperature superconducting powder was prepared in a nitric acid solution containing excess oxalic acid with a mass ratio of Y, Ba, and Cu of 1:1:3 at pH=1.0~1.4. Use nitrates of Y, Ba, and Cu as raw materials, add oxalic acid, and perform co-precipitation at pH=2~4. The prepared precursor is thermally decomposed at 850~930°C to prepare high-temperature superconducting powder with Tc=92 K. . Nitrate is added to the mixture of oxalic acid and ethanol according to the material mass ratio of Bi:Pb:Sr:Ca:Cu: 0.8:0.2:1:1:2, and the pH value is adjusted with ammonia water. The obtained precursor is heated at 800°C. After roasting for 6 hours, Bi-Pb-Sr-Ca-Cu-O high-temperature superconducting powder was obtained. Bi-Pb-Sr-Ca-Cu-O superconductor powder was prepared by microemulsion method, with particle size in the range of 2 to 6 nm. The uniform nanoparticles of superconductor precursors precipitated in microemulsions can generate microscopically uniform high-density superconductors after heating. The superconductor Tc=112 K shows superior performance than other synthesized superconductors. In the water-CTAB-n-butanol-octane microemulsion system, one contains an aqueous solution of yttrium, barium and copper nitrates, the molar ratio of the three is 1:2:3; the other contains an ammonium oxalate solution as the water phase, By mixing two microemulsions, the product is separated, washed, dried and burned at 820°C for 2 hours to obtain a Y-Ba-Cu-O superconductor with a Tc=93K.
6. Preparation of metal or alloy powder materials
Use Ce (NO3)3· 6H2O (>98%), Y (NO3 sub>)3· 6H2O (99.9%) and C2H2O4· 2H 2O (>99.5% ), using oxalate as precipitation medium. It has been shown that oxalates are not as sensitive to cleaning and drying conditions as hydroxide precipitates, allowing yields close to 100%. After washing the precipitate with alcohol and calcining at 700°C, fine powder with an average agglomeration size of 0.7 μm was obtained. The powder has good compressibility and sinterability. Tungsten-cobalt cemented carbide has excellent mechanical properties, but cobalt is an expensive and scarce metal, so research on substituting cobalt is of great practical significance. Ni/Co composite powder for cemented carbide was prepared using the oxalate co-precipitation method. The powder composition was nNi:nCo=1:1 with a molar ratio of nNi:nCo=1:1 and an average particle size of 3.28 μm. Research shows that the performance of cemented carbide bits made with this composite powder is no less than that of WC-Co cemented carbide.
7. Others
Neodymium metal can be extracted from NdFeB magnetic material manufacturing industrial waste using oxalic acid as a precipitant. Rare earth composite oxide catalysts have good exhaust gas purification performance. Compared with traditional precious metal catalysts, rare earth composite oxide catalysts have low cost and good resistance to lead poisoning. Using the oxalate co-precipitation method and according to different drying conditions, nanocrystalline LaCoO3 perovskite with more oxygen vacancies was obtained. CuC2O4-ZnC2O4·2H2O and conducted thermal analysis research on it, CuC2O4-ZnC2O4· 2H2O is metal oxide, which can be widely used in magnetic materials, ceramic materials, superconducting materials, etc.
[References]
[1] Long Miao, He Runxia, Liu Minyue, et al. Harm of oxalate in feed to ruminants and its prevention [J]. Feed Industry, 2014, 35(12): 48-50.
[2] Zhang Weinan, Chen Donghua. Application of oxalate in inorganic functional materials[J]. Journal of South Central University for Nationalities: Natural Science Edition, 2004, 23(2): 29-32.
[3] Yin Xiaowen, Liu Min, Lai Weihong, et al. Research on the recovery of rare earth elements from NdFeB waste by oxalate precipitation method [J]. Rare Metals, 2014, 38(6): 1093-1098.
[4] Wu Jianhui, Zhang Chuanfu, Wu Linlin, et al. Application of oxalate precipitation method in the preparation of powder materials [J]. Sichuan Nonferrous Metals, 2001 (3): 13-16.
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