Dear Abdulwasiu Salaudeen Olawale

I hope you feel good today. your equation so interesting. The pH parameter so an important parameter for describe mechanism removal of metal. When pH increase, the metal ion will convert to metal oxide ion then undissolved metal (precipitation).

Therefore you should first do the control experiment (add adsorbent with pure water) to understand is your adsorbent dissolves or not such as CaCO3. you should to measurement the final pH to know what happens if increase which means your adsorbent adds OH ion to water.

We look for adsorption mechanisms matter not for precipitation because the precipitation will clog the filter.

you can read the research below :

• Article Predominant mechanisms for the removal of nickel metal ion f...

Dear Abdulwasiu Salaudeen Olawale

I hope you feel good today. your equation so interesting. The pH parameter so an important parameter for describe mechanism removal of metal. When pH increase, the metal ion will convert to metal oxide ion then undissolved metal (precipitation).

Therefore you should first do the control experiment (add adsorbent with pure water) to understand is your adsorbent dissolves or not such as CaCO3. you should to measurement the final pH to know what happens if increase which means your adsorbent adds OH ion to water.

We look for adsorption mechanisms matter not for precipitation because the precipitation will clog the filter.

you can read the research below :

• Article Predominant mechanisms for the removal of nickel metal ion f...

" many metals " Do you mean the hydrated metal cations? If so , look at the pKa of these cations and solubility products. If solution is not buffered then pH is dependent on concentrations and pKa. The precipitation might be controlled by kinetics. The adsorption is also pH dependent. In addition, an adsorbent may change the solution pH. Therefore, it's not simple task to separate adsorption and precipitation. As Laith A. Naji pointed out that precipitation on adsorbent surface may result in an additional complication.

thank you @ Laith Naji and @Yurii V Geletii. my point is, adsorption is pH dependent and metal precipiation is also pH dependent e.g Fe3+ precipitate at pH of 3, Cr precipitate at pH of 5, Cu precipitate at pH of 6, Zn precipitate at pH of 7, NI precipitate at pH of 8, Pb precipitate at pH of 8.5, Cd precipitate at pH of 8.2. with this it will be very wrong to conclude that metal removal at these pHs is entirely due to adsorption when we know these metals will precipitate at those pHs

Abdulwasiu Salaudeen Olawale ,

you are absolutely right "that metal removal at these pHs is entirely due to adsorption."

My point " Therefore, it's not simple task to separate adsorption and precipitation."

The precipitation is governed by the solubility product and will happen once the activity of metal ion and that of hydroxyl ions reach the threshold level. On the other hand, adsorption will occur even if, the activity is far below the solubility product. Therefore, removal of metals by precipitation does not ensure complete removal of metal ions.

@Prakash Chandra, yes removal of metals by precipitation does not ensure complete removal of metal ions. At the pH of precipitation, metal removal is not entirely due adsorption. Thanks

Dear Abdulwasiu Salaudeen Olawale

I hope you feel well today. If you want to separate these mechanisms to know the removal of adsorption and precipitation you can to follow the method in the link below :

Article Predominant mechanisms for the removal of nickel metal ion f...

But when we study the adsorption mechanism, we avoid that value of pH because we want to separate the metal from liquid to solid for easy control and recovery metal.