Background and overview[1]
Oxalic acid is also known as “ramic acid” and its scientific name is “oxalic acid”. The molecular formula is (COOH)2·2H2O. It is a colorless and transparent monoclinic crystal, often found in rhubarb and other plants in the form of calcium salts. It is highly acidic and not easy to burn. Relative density: 1.653 (19℃/4℃); melting point: 101.5℃; sublimation point: 150~160℃, toxic, soluble in hot water, ethanol and glycerin, slightly soluble in ether, harmful to eyes and harmful to skin The corrosive effect is stronger when exposed to water. People who take 2 grams in the mouth can be poisoned and die. During storage, it should be protected from moisture, rain, and isolated from oxidants and alkali substances. The storage and transportation temperature should not be higher than 40℃. To prevent contact with food, it should be kept away from living areas and should not be installed on the deck when loading the ship. Although this substance is not easy to burn, if it causes fire, water and sand can be used as fire-fighting methods. If it enters your eyes or touches your skin, rinse with plenty of water. If swallowed by mistake, you should be sent to the hospital for treatment. Industrially, it is generally synthesized from carbon monoxide and sodium hydroxide. The main producing areas in my country are Shanghai, Tianjin, Mudanjiang, Zhuzhou, Lianyungang, Wuhan, Chengdu, Guangzhou, Nanjing, Ningbo and Xuzhou. The annual export volume is more than 10,000 tons, mainly sold to the United States, Japan, Hong Kong, Singapore, and Pakistan. countries and regions such as Stanton and the European Community.
Apply[2-5]
Oxalic acid can be used as a solvent for refining rare metals, a dye reducing agent, a printing and dyeing bleaching agent, a pp adhesion promoter, a metal rust remover, a marble polishing agent, a descaling agent, and an anti-wrinkle surface treatment agent for paper. , raw materials for organic synthesis. Some research results show that exogenous oxalic acid can effectively delay the postharvest ripening process of melons, winter dates, kiwis, peaches, mangoes and apples, thereby extending the storage period and shelf life of the fruits. For example, postharvest hardness, soluble solids (SSC) and titratable acid (TA) content of mango are important indicators for measuring fruit maturity. Postharvest mangoes were soaked in 5 mmol·L-1 oxalic acid solution for 10 minutes and then stored under normal temperature (25°C), low temperature (14°C) and controlled atmosphere (3% CO2 + 2% O2, 14°C) conditions. The fruit softened and SSC increased. and TA decrease rate are significantly slowed down; the fruit storage period is about 20 days at normal temperature (25°C), 6 days longer than the control; at low temperature (14±1)°C, the storage period is 28 days, 7 days longer than the control, and the shelf life is 3 days Above; under controlled atmosphere conditions, the storage period is 30 to 35 days, which is about 10 days longer than the control, and the shelf life can reach 3 days. During fruit ripening, polygalacturonase (PG), pectineesterase (PE), pectin methylesterase (PME), glucanase (α-Gal or/and β-Gal), Hydrolytic enzymes such as xylanase (XYL) and cellulase (Cx) are considered to be important factors causing fruit softening. Our study found that oxalic acid treatment significantly reduced the activities of PG, α-Gal, β-Gal, Cx and XYL in mango pulp. Examples of its application are as follows:
An experiment was conducted to study the effects of exogenous oxalic acid on the relative permeability of cell membranes, changes in glutathione (GSH) and ascorbic acid (AsA) contents, and Ca2+ distribution in pepper leaves under heat stress. The results showed that heat stress increased the relative permeability of mesophyll cell membranes, while oxalic acid treatment reduced the increase. Heat stress reduced the contents of GSH and AsA in leaves; oxalic acid treatment caused a smaller decrease in their contents under heat stress. Calcium pyroantimonate precipitated particles in pepper mesophyll cells are mainly distributed in vacuoles, intercellular spaces and chloroplasts at room temperature. Under heat stress, they are reduced in vacuoles and intercellular spaces, but appear in the nucleus and cytoplasm; in mesophyll cells treated with oxalic acid, pyroantimony Calcium acid precipitated particles increased significantly in the intercellular space and decreased in the vacuoles.
In addition, after harvesting, kiwi fruits are soaked in 5mmol·L-1 oxalic acid for 10 minutes and placed in a cold storage at (0±0.5)℃, RH90%95% Store for 90 days. The results showed that oxalic acid treatment can alleviate the chilling injury and cell membrane damage of kiwi fruit, delay the decline of hardness and titratable acid, significantly increase the activities of superoxide dismutase (SOD) and catalase (CAT), and maintain high ascorbic acid ( AsA) and glutathione (GSH) content, reduce the generation rate of superoxide anion free radicals (O2–) and hydrogen peroxide (H2O2) content, maintaining high ATP content and energy charge level, indicating that oxalic acid treatment can maintain good fruit quality and enhance the cold resistance of the fruit, which may be related to improving the antioxidant of the fruit. The ability to maintain higher ATP is related to energy charge.
In addition, oxalic acid auxiliary enhanced acid leaching method is used to extract iron from sulfuric acid slag. The iron oxides in sulfuric acid slag have poor activity and are difficult to recycle efficiently. Moreover, the currently reported additive-enhanced acid leaching method has problems such as the large amount of additives and the easy generation of harmful gases such as H2S. The leaching rates of phosphate and iron still need to be further improved. In order to solve the above problems, this article screened and determined oxalic acid as a more suitable acid leaching additive based on the proposed additive selection principle, and conducted a preliminary discussion on its mechanism of action as an acid leaching additive. Through single-factor condition experiments and orthogonal experiments, the more suitable acid leaching process conditions were investigated and determined: reaction time 7.5h, oxalic acid additive dosage 20%, sulfuric acid leaching liquid mass fraction 50%, reaction temperature 98°C. Under these conditions, the leaching rate of iron in sulfuric acid slag can reach 95.7%. The XRD and EDS analysis results of the sample show that compared with the acid leaching residue without oxalic acid additives, the iron content in the acid leaching residue after adding oxalic acid additives is significantly reduced, indicating that the oxalic acid additives are more effective.The addition obviously promoted the leaching of iron in the sulfuric acid slag.
Main reference materials
[1] Technical Dictionary of Container Transport Business·Volume 2
[2] Effects of oxalic acid treatment on membrane permeability and calcium distribution of pepper leaves under heat stress
[3] Effects of oxalic acid treatment on chilling damage, antioxidant capacity and energy charge of postharvest kiwifruit
[4] Extraction of iron from sulfuric acid slag by enhanced acid leaching with oxalic acid additives
[5] Research progress on the preservation effect and mechanism of exogenous oxalic acid on fruits
