Adsorption of low-concentration ammonium onto vermiculite from hebei province, China - Wang, Mingshan (China University of Geosciences. School of Material Sciences and Technology) ; Liao, Libing (China University of Geosciences. School of Material Sciences and Technology) ; Zhang, Xiuli (China University of Geosciences. School of Material Sciences and Technology) ; Li, Zhaohui (University of Wisconsin - Parkside. Department of Geosciences) ; Xia, Zhiguo (China University of Geosciences. School of Material Sciences and Technology) ; Cao, Weida (China University of Geosciences. School of Material Sciences and Technology)