Hi Noor Ul Ain

Please may different concentrations of Cr(VI) and Pb(II) solutions from standard stocks. Vary the adsorbent dose and set for shaking or adsorption for different time period e.g., 15 min, 30 min, 45 min, 60 min. Measure the final concentration of Cr(VI) or Pb(II) in those. Then you may increase the contact time to find out the equilibrium contact time. These articles may help you:

DOI: 10.1039/D1VA00019E, org/10.1016/j.jece.2020.103759, org/10.1016/j.jes.2019.09.004, .org/10.1021/acsomega.9b00252, org/10.1016/j.jallcom.2017.05.149

Regards

Hi Noor Ul Ain

You can fix the adsorbent dose and the concentrations of Cr(VI) and Pb(II). You can measure the remaining concentrations of Cr(VI) and Pb(II) after certain time intervals, e.g. 10, 30, 60, 90, 120 min, and so on, until you achieve adsorption equilibrium.

For Cr(VI) you may seek help from the following article.

Article Underwater suspended bifunctionalized polyethyleneimine-base...

There is no fixed time for the Adsorption of metal, try to vary the time with a constant known concentration and other variables

One thing I've learned from my experiments is that you need to get your adsorbents in contact with the heavy metals. In this way, you can take readings at certain times and form the adsorption capacity graph over time. When the adsorption capacity remains constant, you have reached the maximum in the given time.

Hi

parameter optimization under your working conditions is important. you need to check the removal efficiency of your synthesized membrane by varying the time from let say 5- 75 minutes with equal intervals. then you will be able to get a tend/ optimized result for the time required for removing the maximum amount of heavy metals using membrane in batch mode.