阅读说明：本技术 一种生产高纯度重铬酸铵并联产多用途氧化铬绿的方法 (Method for producing high-purity ammonium dichromate and producing multipurpose chromium oxide green ) 是由 张忠元 谢希智 孔红霞 陈荣 胡兴鹏 程耀 于 2019-10-22 设计创作，主要内容包括：本发明公开了一种生产高纯度重铬酸铵并联产多用途氧化铬绿的方法,属于铬盐生产领域。包括如下步骤：S1、将铬酸酐加水配置成铬酸溶液；S2、按照理论量在铬酸溶液中分别缓慢加入碳酸氢铵、碳酸铵或氨水等铵类化合物；S3、物料全部加完后,通过加水或者蒸发等方式控制料液波美度40-42波美之间；S4、搅拌下冷却结晶,待料液中晶体固相达到料液浓度一半以上后,离心分离得到高纯度重铬酸铵产品；母液仍为重铬酸铵溶液,返回继续用于下组物料的配料过程。本发明应用于工业化生产,达到企业增效、减排、降低污染的目的。(The invention discloses a method for producing high-purity ammonium dichromate and co-producing multipurpose chromium oxide green, belonging to the field of chromium salt production. The method comprises the following steps: s1, adding water into chromic anhydride to prepare chromic acid solution; s2, slowly adding ammonium compounds such as ammonium bicarbonate, ammonium carbonate or ammonia water and the like into the chromic acid solution according to the theoretical amount; s3, after all the materials are added, controlling the Baume degree of the feed liquid to be between 40 and 42 Baume through water adding or evaporation and other modes; s4, cooling and crystallizing under stirring, and after the solid phase of crystals in the feed liquid reaches more than half of the concentration of the feed liquid, performing centrifugal separation to obtain a high-purity ammonium dichromate product; the mother liquor is still ammonium dichromate solution and returns to be continuously used in the material proportioning process of the next material. The invention is applied to industrial production, and achieves the aims of enterprise efficiency improvement, emission reduction and pollution reduction.)

1. A method for producing high-purity ammonium dichromate and producing multipurpose chromium oxide green is characterized by comprising the following steps: the method comprises the following steps:

s1, adding water into chromic anhydride to prepare chromic acid solution;

s2, slowly adding ammonium compounds such as ammonium bicarbonate, ammonium carbonate or ammonia water and the like into the chromic acid solution according to the theoretical amount;

s3, after all the materials are added, controlling the Baume degree of the feed liquid to be between 40 and 42 Baume through water adding or evaporation and other modes;

s4, cooling and crystallizing under stirring, and after the solid phase of crystals in the feed liquid reaches more than half of the concentration of the feed liquid, performing centrifugal separation to obtain a high-purity ammonium dichromate product; the mother solution is still ammonium dichromate solution and returns to be continuously used for the batching process of the next material;

s5, the produced high-purity ammonium dichromate is self-ignited and roasted in a rotary kiln.

2. The method of claim 1, wherein the method comprises the steps of: in the step S2, for each unit mass of chromic anhydride, the consumption amount of the industrial ammonia water with the mass fraction of 33-35% is the same as that of the chromic anhydride, wherein the mass of the theoretical consumption of ammonium bicarbonate is 80% of that of the chromic anhydride, and the mass of the ammonium carbonate is 50% of that of the chromic anhydride.

Technical Field

The invention belongs to the field of chromium salt production, and particularly relates to a method for producing high-purity ammonium dichromate and producing multipurpose chromium oxide green.

Background

The ammonium dichromate is orange monoclinic crystal. It is easily soluble in water and ethanol, and insoluble in acetone. The method is mainly used for the production of chromium oxide green, organic synthesis catalysts, mordants, developing solutions and the like. The traditional ammonium dichromate is generally prepared by reacting sodium dichromate with ammonium sulfate and ammonium chloride, evaporating and concentrating, cooling, crystallizing and washing. But has the problems of large wastewater discharge, high chlorine radical in the wastewater, high post-treatment cost and the like, and the product purity is not high.

Chromium oxide (Cr) ₂O ₃) Is the basic component of green inorganic pigments, which are also important green pigments (chromium oxide green). The product has the advantages of good stability, acid and alkali resistance, high temperature resistance, light and weather resistance and the like, and is widely applied to the production of products such as metallurgy, paint, coating, printing ink, plastics, rubber, chemical fiber, textile, ceramics, glass, cement and the like, and the industries such as cosmetics, food, adhesives, electrostatic copying and the like.

Currently, the industrial production of chromium oxide green mainly adopts a chromic anhydride thermal decomposition method and ammonium sulfate-sodium bichromate thermal decomposition (U.S. Pat. No. 4,40860). The thermal decomposition method of chromic anhydride is the main production method of chromium oxide green in the traditional production process of chromium salt, and is adopted by most chromium compound production enterprises in China. Although the method has simple process, the pollution problem of yellow smoke containing hexavalent chromium in the thermal decomposition process of chromic anhydride cannot be ignored. The preparation of chromium oxide by ammonium sulfate-sodium bichromate thermal decomposition method is the most comprehensive production method with the highest output in foreign countries. The method is suitable for large-scale production of rotary kilns, has little harmful gas in the production process, but has high requirements on equipment and high sulfur content of products, and simultaneously, because the ammonium sulfate-sodium bichromate thermal decomposition method is a mixed system of chromium oxide and sodium sulfate in the materials, the products need to use a large amount of water to wash water-soluble salt, so that the environmental problems of large wastewater discharge amount, high subsequent salt-containing wastewater treatment cost and the like are caused.

In the existing method for producing pigment chromium oxide green, sodium bichromate and ammonium sulfate are used as raw materials, and the reaction is carried out to remove the generated ammonium dichromate and generate sodium sulfate to form a mixed phase. The direct roasting is a mixed system of chromium oxide green and sodium sulfate, and a chromium oxide green product is produced by further washing. The production process has the advantages of large environmental risk, high water treatment cost, high impurity sulfur content of the product and single product application, and can only be applied to pigment varieties and cannot be applied to the fields of metallurgical grade and the like.

Disclosure of Invention

The invention aims to provide a method for producing high-purity ammonium dichromate and producing multipurpose chromium oxide green.

The invention adopts the following technical scheme: a method for producing high-purity ammonium dichromate and producing multipurpose chromium oxide green comprises the following steps:

s1, adding water into chromic anhydride to prepare chromic acid solution;

s2, slowly adding ammonium compounds such as ammonium bicarbonate, ammonium carbonate or ammonia water and the like into the chromic acid solution according to the theoretical amount;

s3, after all the materials are added, controlling the Baume degree of the feed liquid to be between 40 and 42 Baume through water adding or evaporation and other modes;

s4, cooling and crystallizing under stirring, and after the solid phase of crystals in the feed liquid reaches more than half of the concentration of the feed liquid, performing centrifugal separation to obtain a high-purity ammonium dichromate product; the mother solution is still ammonium dichromate solution and returns to be continuously used for the batching process of the next material;

s5, the produced high-purity ammonium dichromate is self-ignited and roasted in a rotary kiln.

Further, in the step S2, for each unit mass of chromic anhydride, the theoretical consumption amount of ammonium bicarbonate is 80% of the mass of chromic anhydride, the mass amount of ammonium carbonate is 50% of the mass of chromic anhydride, and the consumption amount of 33-35% of industrial ammonia water is the same as the mass amount of chromic anhydride.

The raw materials of the invention are chromic anhydride, water, ammonium bicarbonate, ammonium carbonate or ammonia water, the reaction generates pure ammonium dichromate, the impurity amount is small, and the low-sulfur metallurgical-grade chromium oxide green product can be produced after roasting.

The invention takes chromic anhydride as raw material, forms chromic acid solution after water dissolving, and then adds NH according to theoretical quantity ₄HCO ₃、（NH ₄） ₂CO ₃Or ammonia water, and reacting to generate an ammonium dichromate solution. The reaction chemical equation is as follows:

CrO ₃+H ₂O==H ₂CrO ₄

2NH ₄HCO ₃+2H ₂CrO ₄==(NH ₄) ₂Cr ₂O ₇+2CO ₂+3H ₂O

（NH ₄） ₂CO ₃+2H ₂CrO ₄==(NH ₄) ₂Cr ₂O ₇+CO ₂+2H ₂O

2NH ₃·H ₂O+2H ₂CrO ₄==(NH ₄) ₂Cr ₂O ₇+3H ₂O

and preparing a solution to enable the Baume degree to reach 40-42 Baume, cooling, crystallizing and centrifugally separating to obtain pure ammonium dichromate. The mother liquor is still ammonium dichromate solution and is continuously used for the batching reaction of the next procedure. No wastewater is discharged in the whole production process, the product purity is high, and the yield reaches more than 99%.

According to the invention, ammonium compounds such as ammonium bicarbonate, ammonium carbonate and ammonia water react with chromic anhydride with the content of 99.8% (national standard, industrial chromic anhydride GB 1610-2009 excellent product content is more than or equal to 99.8%, first-class product content is more than or equal to 99.6%) to produce ammonium dichromate with the content of more than or equal to 99.8% by a crystallization method. The reaction can be carried out at normal temperature for 2 hours. The reaction condition is low, and the continuous industrial production can be realized.

The method utilizes the produced high-purity ammonium dichromate to carry out spontaneous combustion roasting in a rotary kiln (the ammonium dichromate is extremely easy to combust and release heat without providing other combustion energy sources), and the chromium oxide green product produced by the method has extremely low carbon and sulfur contents due to high purity of the ammonium dichromate, and can be directly used for producing high-purity metal chromium products from metallurgical-grade chromium oxide green; meanwhile, the chromium oxide green product produced by roasting ammonium dichromate is widely applied to abrasive-grade, refractory-material-grade and high-end pigment-grade chromium oxide green products due to high particle concentration, small particle size, uniform distribution and easy adjustment and control of hue (products with different colors can be produced by adjustment according to customer requirements at different roasting temperatures). The chemical reaction equation of the decomposition process is as follows:

the reaction process can obtain chromium oxide green with the content of more than 99 percent without washing with water after direct roasting because the ammonium dichromate has high purity, the carbon content of the product is less than 0.01 percent, and the sulfur content is less than 0.01 percent, thereby reaching the production standard of metallurgical-grade chromium oxide green products.

The invention is applied to industrial production, and achieves the aims of enterprise efficiency improvement, emission reduction and pollution reduction.

Detailed Description

The present invention will be further described below, and it should be noted that the following examples are provided to illustrate the detailed embodiments and specific procedures based on the technical solution, but the scope of the present invention is not limited to the examples.