Removal of Methylene Blue from Aqueous Solution by Mixture of Reused Silica Gel Desiccant and Natural Sand or Eggshell Waste oleh Tatjana Juzsakova, Ali Dawood Salman, Thamer Adnan Abdullah, Rashed Taleb Rasheed, Balázs Zsirka, Rasha R. Al-Shaikhly, Brindusa Sluser, Igor Cretescu