Goetz Baumgarten

Nanofiltration of nitric acidic solutions from picture tube production

Abstract In this paper the pilot tests of a recycling process for removing lead form nitric acid solutions have been presented. At first batch tests were performed. Permeate yields up to 80% could be achieved in these tests. Corresponding to these yields the lead concentrations rose up to 70 g/l. Due to the saturation limit of lead salts at about 75 g/l no higher yields could be achieved without precipitation of the lead salts. Altering a washing step of the production avoided the input of free silicic acid into the nitric acid solution. This step ensured that there was no fouling of the membranes due to the precipitation of silicon dioxide. Continuous tests showed that the permeate flows and the lead rejection rates remained stable over a long period of time. After successful completion of the pilot tests the concept has been realized on technical scale. Using the nanofiltration it is now possible to recycle approximately 80–90% of the nitric acid, which formerly had to be exchanged. In addition to the reduced need for fresh acid for the etching process, the alkali needed for neutralizing the waste acid stream could also be drastically reduced. As an added benefit the nitrate load of the remaining waste water was also decreased.

Nanofiltration of CIP waters from iodine X-ray contrast media production: process design and modelling

Abstract CIP (cleaning in place) waters from X-ray contrast material production cause considerable disposal costs as for discharge of iodine-containing effluents; a legal limit of only 1 ppm. AOX has to be met. Therefore, CIP waters which typically contain more than 1000 ppm are currently incinerated, thus requiring a huge amount of energy. A two-stage nanofiltration process consisting of an enrichment and a purification step was designed for separating contrast agents out of rinsing waters. Required areas for both stages were exemplarily calculated. Rejection was greater than 99% at transmembrane pressures of 20–40 bar and resulting fluxes of up to 200 L/(m2h). Besides designing an economically feasible nanofiltration process which yields a permeate with concentrations below the legal limit and a retentate of much less volume for incineration, the aim of this project was to further application of mathematical model descriptions of NF transport phenomena and to find an appropriate design equation. It could be shown that in this case concentration polarisation or gel layer formation were of minor importance. As adsorption appeared to cause the principal resistance to both solvent and solute flux, parameters of an extended solution-diffusion model were fitted in such a way that they account for this physical effect.