Mechanism and kinetics of iron removal in Fe-Al-H2SO4 system by coordination precipitation

Abstract

The highly selective removal of iron in the strong acid solution system is an important operation link in industrial production and wastewater treatment. The removal technology is related to the production cost and product quality. N,N-Diethylammonium O,O′-Dicyclohexyldithiophosphate (DADCDP) as an organic coordination precipitation agent was employed to remove iron in the sulfuric acid solution system. The results showed that iron is removed successfully in the iron-aluminum mixed solution with high selectivity with the use of DADCDP, and the removal rate is reached to 99.8% while the aluminum loss is less than 2.0%. By analyzing the content of the solution components and the morphology of the product, combined with the theory of coordination chemistry, it is inferred that the complexes with a coordination number of 4 mainly generated when Fe3+ is complexed and precipitated using DADCDP. The entire reaction process is mainly composed of the rapid reaction stage controlled by the chemical reaction and the slow reaction stage controlled by solid-phase diffusion. The activation energy of the rapid reaction stage and the slow reaction stage are 2161.31 J·mol−1 and 5207.52 J·mol−1, respectively.