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We present an experimental study of the electrokinetic properties of a model colloidal system in which the number of ionizable sites per particle is controlled by exploiting the competitive adsorption between a ionic and a nonionic amphiphile. The adsorption of the nonionic amphiphile is monitored by light scattering. By measuring the electrophoretic mobility, we obtain the zeta-potential ζ of the particles. We find that ζ is independent from the ionic strength and strongly dependent on the surface density of ionizable sites. This indicates that in our system we can separately control zeta potential and ionic strength. In the investigated range of ionic strength and particle concentration, the Kerr constant of the dispersion is found to be proportional to the particle concentration, and does not contain any significant collective effect. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The physical, chemical and mineralogical characterization of the constituents of magnesium-rich synthetic gypsum produced in a rare earth-refining plant located in Gebeng, Pahang, Malaysia was conducted through elemental chemical analysis, scanning electron microscopy with Energy Dispersive X-ray (EDX)-analyzer, thermal analysis, X-ray fluorescence and X-ray diffraction. The crystalline nature of the by-product was studied using FTIR spectroscopy. Elemental analysis confirmed the presence of Ca and Mg, which are essential macronutrients required by plants and this Ca alongside the high pH (9.17) of MRSG may confer on the material a high acid neutralization capacity. From the result, it was observed that the studied by-product is a heterogeneous crystalline material comprising of gypsum (CaSO4.2H2O) and other major components such as calcium (magnesium) compounds (hydroxide, oxide, silicates, and carbonate) and sulfur. These aggregates may contribute to give an acid neutralization capacity to MRSG. The XRD study of MRSG indicated a high content of gypsum (45.4%), shown by the d-spacing of 7.609 Å (2-theta 11.63) in the diffractogram. The infrared absorption spectra of MRSG indicate close similarities to mined gypsum. The results of the characterization indicated that MRSG has valuable properties that can promote its use in amending soil fertility constraints on nutrient-deficient tropical acid soils. [ABSTRACT FROM AUTHOR]

The study evaluates pollution by Pb, Zn, and Cr, and a possible sustainable solution through phytoremediation technologies, in the surroundings of Haina, a very polluted area of the Dominican Republic. Soils and plants were analyzed at 11 sampling points. After sample processing, the elemental composition was analyzed by ICP-OES. Soil metal concentrations, contaminating factors, pollution load indexes, and the Nemerow pollution index were assessed. Soil metal concentrations showed Pb > Zn > Cr, resulting in very strong Pb pollution and medium-impact Zn pollution, with an anthropogenic origin in some sites. This means that some agricultural and residential restrictions must be applied. Accumulation levels in plant tissues, bioaccumulation factors in roots and shoots, and translocation factors were determined for Acalypha alopecuroidea, Achyranthes aspera, Amaranthus dubius, Bidenspilosa, Heliotropium angiospermum, Parthenium hysterophorus, and Sida rhombifolia. The vast majority of the plants showed very low levels of the potentially toxic elements studied, although it may be advisable to take precautions before consumption as they are all considered edible, fodder, and/or medicinal plants. Despite their low rate of bioaccumulation, most of the plants studied could be suitable for the application of phytoremediation of Zn in the field, although further studies are needed to assess their potential for this. [ABSTRACT FROM AUTHOR]