Treatment of Spent Pickling Solutions by Diffusion Dialysis Using Anion-Exchange Membrane Neosepta-AFN

Comparison of Anion-Exchange Membranes for Diffusion Dialysis of Mixtures of Acids and Their Iron Salts

This study presents the possibility of using diffusion dialysis for the separation of inorganic acids (hydrochloric, nitric, and hydrofluoric) and their ferric salts whose composition corresponds to that of real spent pickling solutions. At a steady state, the transport properties of three different anion-exchange membranes (Fumasep-FAD, Neosepta-AFN, and Neosepta-AHA) are compared using a continuous counter-current dialyzer. At a constant composition of the solutions (acid concentration 3 mol L-1 and iron concentration 30-40 g L-1), the effects of volumetric liquid flow rates on the transport rate of H+ and Fe3+ ions through the membrane are studied. The dialysis process is characterized by the recovery of acids and the rejection of salts. Furthermore, the values of the dialysis coefficients of acids, iron, and the acid/iron separation factors are calculated and compared. The volumetric flow rates of the inlet streams change in limits from 3 × 10-8 to 6 × 10-8 m3 s-1 (from 3 to 6 L h-1 m-2, relative to the membrane area). A comparison of the tested membranes shows slightly better results for acid recovery, iron rejection, and acid/iron separation factors for the Fumasep-FAD membrane than for the Neosepta-AFN membrane. However, the results obtained show that both of these anion-exchange membranes can be considered good separators for tested mixtures that simulate real spent pickling solutions, and there is a good precondition for using diffusion dialysis for processing these solutions in industrial practice. On the contrary, very low values of acid recovery and the overall dialysis coefficient of acid are found for the Neosepta-AHA membrane in the test range of the volumetric flow rate, and, thus, this membrane is insufficient for the adequate separation of these acids and iron salts.

Treatment of Stainless Steel Rinse Waters Using Non-Dispersive Extraction and Strip Dispersion Membrane Technology

The extraction of Fe(III), Cr(III), and Ni(II) from stainless steel rinse water using non-dispersive extraction and strip dispersion membrane technology was carried out in a microporous hydrophobic hollow-fibre module contactor. The fibres were of polypropylene, whereas the organic extractant DP8R (bis(2-ethylhexyl) phosphoric acid) diluted in ExxsolD100 was used as the carrier phase. The rinse water containing the three elements was passed through the tube side, and the pseudo-emulsion formed by the organic phase of DP8R in Exxol D100 and an acidic strip solution were passed through the shell side in a counter-current operation; thus, a unique hollow fibre module was used for extraction and stripping. In non-dispersive extraction and strip dispersion technology, the stripping solution was dispersed into the organic membrane solution in a vessel with an adequate mixing device (impeller) designed to form strip dispersion. This pseudo-emulsion was circulated from the vessel to the membrane module to provide a constant supply of the organic phase to the membrane pores. Different hydrodynamic and chemical variables, such as variation in feed and pseudo-emulsion flow rates, strip phase composition, feed phase pH, and extractant concentration in the organic phase, were investigated. Mass transfer coefficients were estimated from the experimental data. It was possible to separate and concentrate the metals present in the rinse water using the non-dispersive extraction and strip dispersion technique.

Anion Exchange Membrane Based on BPPO/PECH with Net Structure for Acid Recovery via Diffusion Dialysis

In order to improve the performance of the anion exchange membrane (AEM) used in acid recovery from industrial wastewater, this study adopted a new strategy in which brominated poly (2,6-dimethyl-1,4-phenyleneoxide) (BPPO) and polyepichlorohydrin (PECH) were used as the polymer backbone of the prepared membrane. The new anion exchange membrane with a net structure was formed by quaternizing BPPO/PECH with N,N,N,N-tetramethyl-1,6-hexanediamine (TMHD). The application performance and physicochemical property of the membrane were adjusted by changing the content of PECH. The experimental study found that the prepared anion exchange membrane had good mechanical performance, thermostability, acid resistance and an appropriate water absorption and expansion ratio. The acid dialysis coefficient (U_H⁺) of anion exchange membranes with different contents of PECH and BPPO was 0.0173-0.0262 m/h at 25 °C. The separation factors (S) of the anion exchange membranes were 24.6 to 27.0 at 25 °C. Compared with the commercial BPPO membrane (DF-120B), the prepared membrane had higher values of U_H⁺ and S in this paper. In conclusion, this work indicated that the prepared BPPO/PECH anion exchange membrane had the potential for acid recovery using the DD method.