EDTA and Fe(III)-EDTA adsorption on post-vanillin lignin during its precipitation

In the work, we investigated the adsorption of EDTA, Fe3+ ions, and the Fe( III)EDTA complex in the presence and absence of its components, i.e. non-co mplexed EDTA or Fe3+ on post-vanillin lignin. The adsorption was conducted during lignin precipitation from neutral solutions with concentrated HCl. U nder these conditions, all the investigated substances were adsorbed on lig nin, at different compositions of the solutions. The highest, nearly 100% a dsorption efficiency was observed in the case of Fe(III)-EDTA, which was ad sorbed in the presence of Fe3+ ions. This complex was also well adsorbed fr om other solutions, often with an efficiency exceeding 90 %. The Fe3+ ions' efficiency was lower and the adsorption of EDTA was the lowest. Analysing the obtained isotherms with Freundlich's and Langmuir's equations and from the point of view proposed by Giles et ai., we stated that the adsorption p rocesses investigated had a physical. character. Good adsorbing properties of lignin in relation to the investigated substances, as well as the physic al character of the processes, indicate its possible application to wastewa ter purification from EDTA and Fe3+ ions, especially in the form of the Fe( III)-EDTA complex. Particularly interesting may be the proposal of EDTA rem oval after its complexation by addition of a small excess of Fe3+ to the wa stewater, which would enable to remove the trace amount of EDTA at a concen tration of about 0.0008 mole/dm(3), with 93% efficiency.