I am preparing activated carbon from a sludge-based precursor by dry impregnation with K2CO3.
However, after activation when the acid wash was performed on the prepared product, it imparted greenish-blue color.
1. What could be the reason for that?
2. If it is unreacted K (Potassium), how to wash it off?
Dear Ayushi Jaiswal thank you for your interesting technical question. According to the research article cited below, hot water is best to remove residual K2CO3 from your activated carbon. In this paper it is stated: "After carbonization, the sample was cooled down under nitrogen (N2) flow and was washed sequentially several times with hot water, and finally with cold distilled water to remove residual chemicals. Then the sample was dried at 110°C."
Preparation and characterization of activated carbon from palm shellby chemical activation with K2CO3
Article Preparation and Characterisation of Activated Carbon From Pa...
Also please have a look at the following relevant article:
Chars from gasification of coal and pine activated with K2CO3: Acetaminophen and caffeine adsorption from aqueous solutions
Article Chars from gasification of coal and pine activated with K2CO...
In this paper "After cooling, under N2 flow, the samples were washed with distilled water up to pH 7 and dried at 100 °C."
I assume that the greenish-blue color is due to some small amount of organic impurity.
Ayushi Jaiswal I also noticed that greenish-blue color for acid washing the created biochar... but I used KOH instead of K2CO3
Deborah C. Crominski da Silva Medeiros What are your opinions regarding the greenish-blue color and have you found any literature where it has been reported?
Colour imparted may be from the raw material sludge use to prepare.
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