Structural alterations of synthetic allophane under acidic conditions: Implications for understanding the acidification of allophanic Andosols

•Allophane is readily dissolved in acidic conditions, especially in pH < 3.0.•Destruction of allophane structure decreases the porosity of allophane.•A conceptual model regarding allophane changes in acidic conditions is proposed.•Better understanding of the behavior and properties of allophane in acidified allophanic Andosols.