Abstract Three clay samples with different mineral compositions (kaolinite, smectite-kaoline, and smectite- rich) were used for zeolite synthesis using the method of hydrothermal reactions after fusion with NaOH. The conditions of hydrothermal crystallization (zeolitization) were found to be at temperature of 100˚C, and time span between 72 h and 96 h for kaoline and smectite-rich samples, while 48 h for the smectite-kaolinite sample. The results indicate that zeolites began to crystallize from clay samples after 48 h, and crystallization increased with increasing time. The synthetic materials have been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), fourier transform infrared spectroscopy (FT-IR) and thermogravimetric (DTA/TGA) analysis. The results indicate that low silica NaX-faujasite type with well-developed octahedral and cubic crystals was synthesized from the three samples. No big difference in the characterization between the three synthetic materials was detected, but smectite-kaolinite sample as raw material was relatively better in crystallization of synthetic zeolite. Applications of the synthetic materials in the removal of heavy metals proved that the synthetic faujasite has strong effect for removing of Cr3+, Co2+, Ni2+ and Mn2+ from aqueous solution.

Abstract Three clay samples with different mineral compositions (kaolinite, smectite-kaoline, and smectite- rich) were used for zeolite synthesis using the method of hydrothermal reactions after fusion with NaOH. The conditions of hydrothermal crystallization (zeolitization) were found to be at temperature of 100˚C, and time span between 72 h and 96 h for kaoline and smectite-rich samples, while 48 h for the smectite-kaolinite sample. The results indicate that zeolites began to crystallize from clay samples after 48 h, and crystallization increased with increasing time. The synthetic materials have been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), fourier transform infrared spectroscopy (FT-IR) and thermogravimetric (DTA/TGA) analysis. The results indicate that low silica NaX-faujasite type with well-developed octahedral and cubic crystals was synthesized from the three samples. No big difference in the characterization between the three synthetic materials was detected, but smectite-kaolinite sample as raw material was relatively better in crystallization of synthetic zeolite. Applications of the synthetic materials in the removal of heavy metals proved that the synthetic faujasite has strong effect for removing of Cr3+, Co2+, Ni2+ and Mn2+ from aqueous solution.

Th e fl ora and fauna of Arabia, particularly southern Yemen, has recently attracted the interest of many authors. In this study, the genus Heliotropium L. (Boraginaceae) is taxonomically revised in southern Yemen. Ten species are recognized. Nomenclature, typifi cation, representative specimens and a diagnostic key to all species are provided, along with their distribution in southern Yemen. Th e taxonomically most valuable characters in the genus are those of fl owers (calyx,corolla, androecium and gynoecium) and nutlets, and those characters are thoroughly investigated and discussed. Both light and scanning microscopy are used in the investigation. Papillate anther apices (brush-like) were recognized in some species. Connate anthers and deep or shallow ventral circular depressions on the nutlets were found to be useful in distinguishing members of H. sect. Orthostachys (viz. H. strigosum , H. rarifl orum and H. ovalifolium ), while winged nutlets were found only in H. pterocarpum . Th e length and hairiness of the style and stigma also proved to be taxonomically useful.

Th e fl ora and fauna of Arabia, particularly southern Yemen, has recently attracted the interest of many authors. In this study, the genus Heliotropium L. (Boraginaceae) is taxonomically revised in southern Yemen. Ten species are recognized. Nomenclature, typifi cation, representative specimens and a diagnostic key to all species are provided, along with their distribution in southern Yemen. Th e taxonomically most valuable characters in the genus are those of fl owers (calyx,corolla, androecium and gynoecium) and nutlets, and those characters are thoroughly investigated and discussed. Both light and scanning microscopy are used in the investigation. Papillate anther apices (brush-like) were recognized in some species. Connate anthers and deep or shallow ventral circular depressions on the nutlets were found to be useful in distinguishing members of H. sect. Orthostachys (viz. H. strigosum , H. rarifl orum and H. ovalifolium ), while winged nutlets were found only in H. pterocarpum . Th e length and hairiness of the style and stigma also proved to be taxonomically useful.