Atmospheric scorodite synthesis reaction was developed. The reaction is oxidation of ferrous ion by oxygen gas in the presence of pentavalent arsenic ion, and synthesized scorodite is well-crystallized in a short retention time of 1 to 7 h. The resulting scorodite particles are as large as 15 μm, with less than 10% in moisture content, and they are readily washed and feature excellent packing properties. This scorodite synthesis process can be incorporated in hydrometallurgy process. The early stage of a mechanism scorodite synthesized in a novel atmospheric process was investigated. Crystalline scorodite was prepared even within 10 min in our novel process. We checked how to build up scorodite crystal by XRD, SEM and TEM. Then at very early stage, string type precipitates were found and after few hours it became plates and octahedron bodies. Environmental leach tests were also performed according to various countries’ batch leaching procedures. The comparisons were made among Japanese, U.S., Canadian, and Dutch leaching tests. In the United States Environmental Protection Agency’s Toxicity Characteristic Leaching Procedure (TCLP) test (method 1311), the obtained scorodite particles released a very low, almost negligible concentration of arsenic in the pH range of 3 to 5, suggesting its long-term stability. In the leach tests of various pH solutions, it was shown that the scorodite solubility was turned greatly by outside environmental factors such as pH rather than long-term stability. In addition, the results showed scorodite released a considerably high concentration of arsenic under specific leaching conditions.
- Oxidation of ferrous ions