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The presence of emerging pollutants such as hazardous chemicals, pharmaceuticals, pesticides, and endocrine-disrupting chemicals in water sources is a serious concern to the environment and human health. Thus, this study focused on exploring the interaction mechanisms between ciprofloxacin (CIP) (antibiotic) and clay (a low-cost adsorbent) during sorption process. Acid activation technique was opted for modifying natural bentonite (NB) to enhance the adsorptive removal of CIP from water. The BET surface area analysis revealed that acid-activated bentonite (AAB) possessed more than two fold higher surface area as compared to NB. Combining pHzpc measurements, effect of solution pH and CIP speciation revealed that CIP sorption onto bentonite is highly dependent on solution pH. Kinetic studies confirmed that CIP sorption mechanism was chemisorption which included ion-exchange and surface complexation mechanisms. The mechanism of CIP sorption onto AAB was successfully explored with the assistance of characterization techniques. Maximal monolayer sorption capacity of AAB was found to be 305.20 mg/g, compared to 126.56 mg/g for NB. Reusability studies demonstrated that AAB could be reused successfully up to 5 cycles. Furthermore, column studies showed satisfactory results confirming that AAB can be successfully used in continuous mode for practical applications. Electronic supplementary material The online version of this article (10.1007/s11356-020-09267-1) contains supplementary material, which is available to authorized users.

Lead (Pb(II)) pollution in water poses a serious threat to human health in many parts of the world. In the past decades, research has been aimed at developing efficient and cost-effective methods to address the problem. In this study, dimethyl sulfoxide (DMSO) and potassium acetate (K-Ac) intercalated kaolinite complexes were synthesized and subsequently utilized for Pb(II) removal from water. The intercalation of kaolinite with DMSO was found to be useful for expanding the interlayer space of the clay mineral from 0.72 to 1.12 nm. Kaolinite intercalation with K-Ac (KDK) increased the interlayer space from 1.12 to 1.43 nm. The surface area of KDK was found to be more than threefold higher as compared to natural kaolinite (NK). Batch experimental results revealed that the maximum Pb(II) uptake capacity of KDK was 46.45 mg g−1 which was higher than the capacity of NK (15.52 mg g−1). Reusability studies showed that KDK could be reused for 5 cycles without substantially losing its adsorption capacity. Furthermore, fixed-bed column tests confirmed the suitability of KDK in continuous mode for Pb(II) removal. Successful application of intercalated kaolinite for Pb(II) adsorption in batch and column modes suggests its application in water treatment (especially removal of divalent metals). Electronic supplementary material The online version of this article (10.1007/s11356-019-06845-w) contains supplementary material, which is available to authorized users.

Water pollution due to emerging contaminants (especially pharmaceuticals) is a major environmental threat which results in the development of antibiotic-resistant bacteria/resistance genes in the aquatic environment. Therefore, robust and cost-effective methods are required to address this problem. In this study, thermal activation was opted for the modification of natural bentonite clay (BC) and utilized to investigate the adsorptive removal of tetracycline (TC) from aqueous solution. The physicochemical surface properties of the raw and modified bentonite samples were also investigated. The BET analysis revealed that the thermally activated bentonite (TB) has better properties than BC. The surface area of TB was found to be more than two-fold higher compared to that of BC. The FTIR spectra exhibited the existence of Al OH, Si O and Si O Si functional groups in the samples, confirming the presence of hydrated aluminosilicate in the clay. The effects of various operating parameters were analyzed via optimization studies. The maximum monolayer adsorption capacity estimated by Langmuir model was found to be 156.7 and 388.1 mg g−1 for BC and TB, respectively. Furthermore, fixed-bed column studies were performed to get insights into the adsorption behavior of TB in a dynamic system. The mechanism of TC adsorption by TB was successfully explored.

Messinian gypsum deposits from Dir El-Baraqan area, Northern Coast of Egypt, were investigated by stable sulfur isotope method, X-ray diffraction, infrared spectroscopy, optical microscopy, and scanning electron microscopy to differentiate features formed under substantial microbial influences as indicator of paleoenvironments. Petrographically, gypsum deposits were classified into three types: biolaminated gypsum, disordered selenite, and swallow-tail selenitic crystals. Biolaminated gypsum is characterized by regular alternating dark and light laminae, which were formed due to the seasonal environmental changes in Dir El-Baraqan area. Stable sulfur isotope data show that the gypsum deposits are characterized by δ34S values ranging from +18.1 to +28.1 ‰. In swallow-tail gypsum, the δ34S values are characterized by a narrow range (from +20.0 to +20.2 ‰) which is considered as the primary phase. In biolaminated gypsum, the δ34S values ranged from +22.8 to +28.1 ‰ which is considered as the secondary phase. However, the white laminae are characterized by δ34S values ranging from +22.8 to +24.1 ‰, while dark laminae are characterized by δ34S values ranging from +27.2 to +28.1 ‰. The high δ34S values of dark laminae revealed the increasing activity of sulfate-reducing bacteria.