Clean production of chromium salts is environmentally friendly and efficient: A note on the synchronous separation technology of aluminum and vanadium in the production process of chromium salts

　　At present, about 120,000 to 150,000 tons of hazardous wastes of chromium-containing aluminum sludge and chromium-containing vanadium-precipitated calcium slag are produced each year in the production of chromium salts in China
.
These waste residues are not only difficult to dispose of, but also cause waste of chromium, aluminum and vanadium resources
.
The synchronous separation technology of aluminum and vanadium in the production process of chromium salts, jointly developed by Sichuan Yinhe Chemical Co.
, Ltd.
, the Institute of Process Engineering of the Chinese Academy of Sciences, and Sichuan Huayida Chemical Co.
, Ltd.
, reduces the source of chromium slag by about 10%, and produces chromium salts.
The cost is reduced by 3% to 5%; combined with the follow-up high-value utilization technology, it is expected to completely absorb the hazardous waste of chromium-containing aluminum sludge and chromium-containing vanadium-precipitated calcium slag and produce high-value products, and the production cost of chromium salt will be reduced by 10% ~15%
.
The process was also selected into the "Petrochemical Green Process Directory (2021 Edition)"
.

　　Reduce environmental risks at the source

　　At present, the existing technology used in the production of chromium salts generally adopts the method of neutralizing and removing aluminum and adding calcium and vanadium to remove aluminum and vanadium in the leaching solution, and by-products chromium-containing aluminum mud and chromium-containing vanadium-precipitating calcium slag
.
In the past few decades, China has vigorously developed and promoted cleaner production technologies in the chromium salt industry.
The Institute of Process Engineering, Chinese Academy of Sciences and Sichuan Yinhe Chemical Co.
, Ltd.
are its representative units
.

　　The synchronous separation technology of aluminum and vanadium in the production process of chromium salts jointly developed by the team includes the technology of rapid neutralization of sodium aluminate and high acid to generate hydroxyaluminum and proprietary equipment, the technology of simultaneous adsorption and removal of aluminum and vanadium, and the weathering water quenching of chromium-containing waste slag.
The preheating aluminum extraction technology has realized the elimination of the source of chromium-containing vanadium precipitation calcium slag, and the source of chromium-containing aluminum mud has been reduced by 23%, which greatly reduces the environmental risk
.

　　Achieve high-efficiency removal of aluminum and vanadium synchronously

　　The synchronous separation technology of aluminum and vanadium in the production process of chromium salt not only realizes the simultaneous and efficient removal of vanadium in the sodium chromate leaching solution and the process of removing aluminum for the first time, but also develops special equipment for the continuous and synchronous removal of aluminum and vanadium in the production of chromium salts to realize the removal of aluminum and vanadium.
The removal rate is greater than 99%, and the vanadium removal rate is greater than 97%
.
In addition, they developed a new technology of slag-returning, weathering, preheating, and water quenching to strengthen aluminum extraction, which greatly improved the conversion stability of aluminum in the chromite reaction process and ensured the stability of the components in the sodium chromate leaching solution
.

　　Compared with the traditional technology, this technology simplifies the traditional four-step removal reaction into one-step reaction in terms of technology, replacing the step-by-step removal process of aluminum removal, calcium addition and vanadium removal that have been used by domestic and foreign industries for nearly 50 years
.

　　From a technical point of view, the simultaneous removal technology of aluminum and vanadium is based on non-classical crystallization theory, through strengthening hydrolysis to control the form of aluminum hydrolysis, and realizes the deep separation of chromium and vanadium.
A breakthrough has been made in the solution
.
In terms of technology, the technology does not introduce other substances in the whole process, and reduces the emission of chromium-containing aluminum sludge and chromium-containing calcium vanadate slag at the source, which is a major innovation in the method of removing impurities in the production of chromium salts
.

　　Significant economic and environmental advantages

　　It is worth mentioning that the use of this process technology in the production process of chromium salts can achieve the dual benefits of improving the resource utilization rate of chromium, aluminum and vanadium and reducing the emission of chromium-containing hazardous wastes
.

　　It is reported that this technology can reduce the production cost per ton of chromium salt calcium-free roasting production technology by 3% to 5%, and the emission of chromium slag per ton of product can be reduced from 0.
8 to 1 ton to 0.
5 to 0.
7 tons, a decrease of 10% to 15%.

.

　　In addition, this technology paves the way for high-value utilization of the associated resources of aluminum and vanadium in chromite
.
At present, the technical team has built a thousand-ton aluminum-vanadium high-value utilization demonstration device using the hydroxy aluminum sludge produced by the aluminum-vanadium synchronous separation technology in the 10,000-ton chromium salt plant, which completely consumes waste and produces a Boehmite products and vanadium products meet the market demand for catalytic cracking catalysts and chemical grade vanadium
.
After technical and economic evaluation, all parties believe that this is a technology with low cost, excellent environment and high added value of products
.

　　After large-scale application in the future, the simultaneous separation and high-value utilization technology of chromium ore co-associated aluminum and vanadium resources is expected to be based on the current clean production technology such as calcium salt-free roasting/liquid phase oxidation of chromium salts.
Solid waste emissions are further reduced by 35% to 40%, and chromium salt production costs are reduced by 10% to 15%
.
After this series of technologies are fully industrialized, compared with foreign chrome salt industries, China's chrome salt industry will gain comprehensive advantages in technology, cost, environmental protection and other fields
.