Desorption was carried out with EDTA, HCl, and NaOH.
It was observed that only 69.76% of the loaded Cr (VI) stripped in 0.1M EDTA and 15.19% stripped with 0.1N HCl, while 87.96% stripped with 0.1N NaOH in the first cycle.
Perhaps due to the speciation of chromium and the surface charge of the adsorbent have changed into the alkaline medium which would weaken the electrostatic interaction between the EMCMCR and the Cr (VI) ions, promoting
desorption.
Hence, further experiments were carried out only with 0.1N NaOH solutions.
Complete desorption was not possible, perhaps due to the involvement of non-electrostatic forces between the EMCMCR and the Cr (VI) ions.
The regenerated EMCMCR was reused for up to 10 adsorption–desorption cycles and the results are illustrated in Fig. 12.
It was found that the adsorption capacity of the EMCMCR was an 8.87% decrease after the first cycle and a 15.40% decrease after the second cycle.
It could still be maintained at 75.73% level at the 10th cycle.
These results showed that the EMCMCR can be successfully regenerated and repeatedly used in Cr (VI) ions adsorption studies without appreciable losses in their adsorption capacities.