Abstract: A new process for preparing feed grade zinc oxide from zinc oxide ore by acid leaching, purification, zinc immersion, filtration, washing and drying to obtain intermediate product basic zinc carbonate and basic zinc carbonate by calcination was studied. The effects of acid leaching, impurity removal conditions and calcination temperature and time on product quality in the preparation process were investigated. The research is a new process for preparing feed grade zinc oxide by the full wet method. It has the advantages of cheap raw materials, good adaptability, low production cost, etc. The quality of the prepared products can reach the HG/T 2792-1996 feed grade zinc oxide first grade product. Standards, the method makes full use of low-grade zinc resources and has a good application prospect.
Key words: zinc oxide ore; acid leaching; purification; calcination; feed grade zinc oxide
Feed grade zinc oxide is an important feed additive and is a fine powder of white or light yellow hexagonal shape. Compared with zinc-containing feed additives such as feed grade zinc sulphate monohydrate and zinc sulphate heptahydrate, feed grade zinc oxide has the characteristics of odorless, non-toxic, fine and fine, high trace element zinc content and fine products, and its bioavailability is high. Is a good source of zinc. Compared with other zinc sources, zinc oxide has a significantly lower cost per unit of zinc, which is beneficial to reduce the cost of feed additives. The amount added is equivalent to 44% of zinc sulfate monohydrate and 28% of zinc sulfate heptahydrate. Studies have shown that zinc from 2000 to 3000 mg/kg of zinc oxide from feed has a growth-promoting and antibacterial effect on piglets, which increases to a reasonable amount and can replace the role of antibiotics. Therefore, feed zinc oxide as a good additive for feed trace element zinc and a substitute for some antibiotics will have a good market prospect [1~3]. In this paper, zinc oxide ore was used as raw material to prepare feed grade zinc oxide in accordance with HG/T 2792-1996 (first-class product) by acid leaching, purification, precipitation conversion, filtration, washing, drying and calcination.
1 Experimental part
1.1 Experimental materials and experimental equipment:
1.1.1 The main raw materials of this experiment are zinc oxide ore, sulfuric acid, sodium carbonate, non-ionized water, etc. The main chemical compositions of zinc oxide ore are shown in Table 1.
Table 1 Main chemical composition of zinc oxide ore
element | Zn | Pb | Fe | SiO 2 | Cu | As | Cd |
Content /% | 57.3 | 4.62 | 2.34 | 0.63 | 1.05 | 0 | 0.56 |
1.1.2 The main instruments of this experiment are: 1000ml three-necked flask, magnetic stirrer, Buchner funnel, constant temperature water bath, constant temperature drying oven, muffle furnace and so on.
1.2 Experimental Principles and Procedures
1.2.1 Zinc Leaching
100 g of zinc ore powder was taken, and a 1000 ml three-necked flask containing a certain amount of sulfuric acid was added thereto, and the mixture was stirred at 80 ° C for 2 hours under constant temperature, and filtered to remove slag. The main elements in the raw materials are mostly in the form of oxides, and the metal oxides have the following reactions:
MOn/2 + nH+ → Mn+ + n/2 H2O
In addition to Zn in the acid leaching process, Pb, Fe, Si, Cu, Cd and other impurity elements are also leached in large quantities. The composition and content of the leaching solution are shown in Table 2:
Table 2 Composition and content of
According to the composition of the leachate, this experiment controls a certain pH value to remove Fe by KMnO4 oxidation water. In addition to Fe, SiO2 is also removed by coprecipitation, adsorption, etc., and Pb, Cu and Cd are removed by zinc powder replacement. The specific process is as follows:
1 oxidized water to remove iron, the leaching solution was added to a 1000 ml three-necked flask, and the KMnO4 solution was slowly added under constant temperature stirring at 80 ° C, and the reaction was stirred for 2 h to control the pH of the solution to 5 to 5.5, and allowed to stand at room temperature for 3 hours, at which time Fe3+ reacted. The Fe(OH)3 precipitate is formed and removed, and the reaction formula is as follows:
5Fe2+ + MnO4- + 8H+ → 5Fe3+ + Mn2+ + 4H2O
Fe3++ 3H2O → Fe(OH)3 ↓+ 3H+
2 Displacement Due to the presence of heavy metal impurities Pb, Cu, Cd in the leachate, the quality of the feed grade zinc oxide product will be seriously affected, so these impurity ions must be removed. In this experiment, zinc powder replacement method is used to remove impurities such as Pb, Cu, Cd in the solution, and no new impurities are introduced. The specific steps are as follows: the Fe filtrate is added to a 1000 ml three-necked flask and divided into two at a constant temperature of 75 °C. The zinc powder is added to the section for purification and purification. In order to ensure the purification of impurities, the total amount of zinc powder is 3 to 4 times of the theoretical amount, and the reaction time of each reaction is 20 to 30 minutes. The displacement reaction equation is as follows:
Me2++ Zn → Zn2+ + Me (Me=Cd, Cu, Pb)
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