ALLOPHANE OF GAMALAMA VOLCANIC SOIL SURFACE MODIFICATION USING SULFURIC ACID: STUDY OF THE EFFECT OF SULFURIC ACID CONCENTRATION. Advanced Research & Development Journal [Internet]. 2026 Feb. 17 [cited 2026 Sep. 12];2(1). Available from: https://www.ardjournal.com/index.php/ard/article/view/71