KHAN, M., M. RIAZ, and K. KHAN. “?EXTRACTION OF ALUMINA FROM NEPHELLINE SYENITE BY SINTERING WITH LIMESTONE”. Biological Sciences - PJSIR, vol. 39, no. 1-4, Feb. 1996, pp. 25-27, https://v2.pjsir.org/index.php/biological-sciences/article/view/2360.