Some researchers say the type of surface electrical charges effects on pH value of the reaction medium and thus the adsorption and removal process , when pH value increases, the overall surface electrical charge on the adsorbents become negative and adsorption process decreases, while if pH value decreases, surface electrical charge become positive and adsorption process increases
Malkoc, E.;Nuhoglu, Y. and Abali,Y. (2006). “Cr (VI) Adsorption by Waste Acorn of Quercus ithaburensis in Fixed Beds: Prediction of Breakthrough Curves,” Chemical Engineering Journal, 119(1): pp. 61-68.
Ali Safaa The removal of micropollutants by adsorption is a surface phenomenon that generally involves electrostatic interactions between the adsorbate and the adsorbent. Therefore, the overall charge at the adsorbant surface has a great influence on the adsorption capacity. It is recommended to determine the pH at the zero charge point of the adsorbents before any adsorption test, as this allows to determine the pH range where the surface of the material is positively and negatively charged. In the case of chromium (VI), it exists mainly in anionic form, so its elimination will take place in the pH zone where the material has a positive surface, i.e. at pH values below pHzc. In general the removal of chromium (VI) by adsorption on biochar, activated carbon or bioadsorbent is optimal at low pH values (2 and 3).
In column study, Time and pH also depend on the space velocity (ratio between Flowrate and amount of adsorbent in the column).
You can find more information about removal of Cr(VI) with column in this research: Article Reductive Adsorption of Chromium(VI) by Coal-Based Activated Carbon
The optimum time and pH for any metal and sorbent combination for sorption will vary so needs to be determined.
You need to start first with flask study to standardize pH. As you mentioned as pH increases the surface charge on the sorbent becomes negative. You can determine the most suitable pH from flask study. The time of equilibration may be determined from from flask study but the time for break through curve in the column may vary.
Try out this article. It may give you the answer. https://scirp.org/journal/articles.aspx/aboutus/paperinformation.aspx?paperid=102532
At lower pH, the adsorption backpedal by H+ ion factor or proton factor and at higher pH, adsorption hampered because of yhe metallic ions start to precipitate as metallic hydroxide or metallic oxide. So it is looking good the pH value near between 4-6, and you should have to study for optimum pH for the removal of particular metal like Cr.
On contrast, time mainly find out the breakthrough time for column study is not so easy like batch study. Here you need to conduct a lot of trial and also need to modeling of Thomas model, Adam-Bohart model, Yoon-Nelson model for the much more accurate BTC curve.
Thank you.
Nearly 4 of pH value is looking good for metallic ion removal from wastewater solution indeed.
- Badges
- Science topic
- Similar topics
- Methodology
- Research Methodology
- Research Papers