1. Existence of Vanadium at Different PH
Vanadate anion or vanadium oxide ion is formed by vanadium oxyacid in aqueous solution. It can exist in various aggregates and form various vanadium oxide compounds. Its properties are very important for the production of vanadium.
The existence of vanadic acid is basically related to two factors. One is the acidity of the solution and the other is the concentration of vanadate. At high alkalinity, vanadate mainly exists. When the aqueous solution is acidified gradually, a series of hydrolysis of vanadate occurs.
When vanadium concentration is very low, such as less than 1 mmol/L, it exists as a single nucleus under various pH conditions. However, vanadate radical has strong polymerization performance. When the concentration of protonated vanadate increases, a series of polymerization will take place. This property is also strengthened with the decrease of pH value.
Vanadate precipitated from alkaline or weak alkaline solution is orthovanadate or pyrovanadate. When the solution is near neutral, tetramer or trimer is precipitated; when the solution is weak alkaline or acidic, polyvanadate is precipitated, and hydration is the polymer, in which protons can be replaced by other metal positive ions. Vanadate ions can also form double salts with other acid ions, such as tungsten, phosphorus, arsenic, silicon, etc., which is one of the sources of vanadate impurities.
2. According to the above analysis, the existing state of vanadium in different PH should be selected according to the existing form of vanadium in different PH. For example, in the solution of PH>8, vanadium exists as a single anion, and resins with strong alkalinity, such as 717 and D201, can be selected. In the solution of PH3-4, vanadium exists in the form of associative acid radicals, which are also negatively charged. We can choose 717, D201 resins, D301R and SPC-23 resins. However, considering the adsorption capacity of resins and the degree of difficulty in desorption, we recommend the products of D301R and SPC-23 represented by weak alkali.
With the decrease of PH and the cationization of vanadium modules, vanadium mainly exists in the form of positive ions and carries positive charges in the strong acid environment of PH < 1. At this time, cation exchange resins such as 732 and D001 should be selected to extract vanadium. However, with the increase of proton number, the influence of hydrogen ions becomes more and more serious. If vanadium is extracted from solution with stronger acidity, it may be necessary to use SPC-20 to chelate vanadium more strongly. Resin will do.
3. It is suggested that, according to the existing state table of vanadium, under the environment of PH-3-4, vanadium ion has stronger binding ability and the highest utilization rate of resin exchange capacity. At this time, weak alkali resin can be used for adsorption, and weak alkali resin itself has larger adsorption capacity. Therefore, for the extraction section of vanadium industry, it is suggested that under the condition of PH-3-4, D301R or SP should be chosen as the best resin. C-23.
