It has been reported that biochars can retain anions, such as nitrate and phosphate. Specific adsorption could explain P retention, but positive charge must be present to electrostatically retain nitrate. pH of zero net charge of some biochars has also been reported at pH 6 to 8, meaning at pH below 6 biochar would carry a lot of positive charge. Oxonium (O-H3+) has been proposed. Yet, from a chemistry standpoint, this cation seems unlikely under normal soil conditions. New explanations for + charge on biochar are appreciated.
Dear Prof. Nguyen Hue,
I visualise about the positive charge of biochar mainly due to presence of alkali and alkaline elements and their compounds formed during pyrolysis process. The main contibutors for positive charge can be Ca, Mg, Potassium etc. But, there is vast scope to look into the charge development and its dynamics vis-a-vis with pyrolysis process/methods, for better application of biochar for different useful purposes.
With best wishes,
Dr. Manish Kumar
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