University of Johannesburg

About: University of Johannesburg is a education organization based out in Johannesburg, South Africa. It is known for research contribution in the topics: Population & Context (language use). The organization has 8070 authors who have published 22749 publications receiving 329408 citations. The organization is also known as: UJ.

The use of low-cost adsorbent (Canola residues) for the adsorption of methylene blue from aqueous solution: Isotherm, kinetic and thermodynamic studies

Abstract: The batch adsorption was carried out to study and investigate pH, initial concentration of MB, adsorbent dosage and contact time. The best efficiency of MB removal by Canola residues were obtained at pH alkaline, dose adsorbent of 3.5 g/L, initial concentration of MB of 25 mg/L and contact time of 75 min. The maximum dye removal was obtained to be 97.5%. As the Canola concentration was increased from 0.5 to 5 g/L, the equilibrium adsorption capacity of Canola (q e ) decreased from 16.7 to 4.87 mg/g, whereas, the MB removal efficiency increased from 33.4% to 97.5%. The adsorption kinetics and equilibrium data were in good agreement with the pseudo-second-order kinetic model and Sips adsorption isotherm respectively. Thermodynamic parameters suggest that the adsorption is a typical physical process, which is spontaneous and endothermic. The study demonstrated that biomass is effective to remove MB under a wide range of experimental conditions.

Precarity and agency through a migration lens

Abstract: This special issue leverages the migrant experience to better understand precarity and agency in the contemporary world. By way of introduction, we examine the broader bodies of literature on precarity and agency, relate them to research on migration, and link them to the contributions in the special issue. Laying a foundation for further research, we illuminate three approaches to study the precarity–migration–agency nexus: an industry-specific approach, a sending country/deportee approach, and a collective action approach. We conclude with a critical analysis of freedom and national borders, considering the ‘open borders’ movement, postnational citizenship, and opposition to marketization.

An actualistic perspective into Archean worlds – (cyano-)bacterially induced sedimentary structures in the siliciclastic Nhlazatse Section, 2.9 Ga Pongola Supergroup, South Africa

Abstract: Extensive microbial mats colonize sandy tidal flats that form along the coasts of today’s Earth. The microbenthos (mainly cyanobacteria) respond to the prevailing physical sediment dynamics by biostabilization, baffling and trapping, as well as binding. This biotic‐physical interaction gives rise to characteristic microbially induced sedimentary structures (MISS) that differ greatly from both purely physical structures and from stromatolites. Actualistic studies of the MISS on modern tidal flats have been shown to be the key for understanding equivalent fossil structures that occur in tidal and shelf sandstones of all Earth ages. However, until now the fossil record of Archean MISS has been poor, and relatively few specimens have been found. This paper describes a study location that displays a unique assemblage with a multitude of exceptionally preserved MISS in the 2.9-Ga-old Pongola Supergroup, South Africa. The ‘Nhlazatse Section’ includes structures such as ‘erosional remnants and pockets’, ‘multidirected ripple marks’, ‘polygonal oscillation cracks’, and ‘gas domes’. Optical and geochemical analyses support the biogenicity of microscopic textures such as filamentous laminae or ‘orientated grains’. Textures resembling filaments are lined by iron oxide and hydroxides, as well as clay minerals. They contain organic matter, whose isotope composition is consistent with carbon of biological origin. The ancient tidal flats of the Nhlazatse Section record four microbial mat facies that occur in modern tidal settings as well. We distinguish endobenthic and epibenthic microbial mats, including planar, tufted, and spongy subtypes. Each microbial mat facies is characterized by a distinct set of MISS, and relates to a typical tidal zone. The microbial mat structures are preserved in situ, and are consistent with similar features constructed today by benthic cyanobacteria. However, other mat-constructing microorganisms also could have formed the structures in the Archean tidal flats.