The adsorption of crystal violet by kaolin

Abstract

The uptake of crystal violet on kaolin was examined over a pH range of 2.5 to 9.5, adsorption showing an increase with pH. The attainment of equilibrium between adsorbate and adsorbent is shown to be a two-stage process, the first stage being synchronous with the release of magnesium from the kaolin lattice. Evidence is presented that the major mechanism of adsorption is by electrostatic charges arising from cation replacement in the clay lattice, and that charges arising from the amphoteric nature of the aluminium atom of kaolin make little contribution to the overall adsorptive process.The adsorption by kaolin of promazine has been reported by Sorby, Plein & Benmaman (1966) and of atropine by Ridout (1968a,b). These workers found the adsorption to be pH dependent. So that the mechanism of adsorption might be established, we have examined the uptake by kaolin of a basic substance, crystal violet, under a variety of experimental conditions. M A T E R I A L S AND M E T H O D SCrystal violet (reagent grade) was used without further purification. Light kaolin (B.P. quality) was dried at 100" (3 h), mixed thoroughly and stored in tightly closed containers. The weight mean diameter of the kaolin was 3.3 pm (sedimentation balance), and the surface area 11.2 m2 g-l (nitrogen adsorption: Perkin-Elmer Shell sorptometer, Model 21 2D). The efect of p H on the adsorption of crystal violet by kaolinTo flasks containing kaolin (2 g) was added 100 ml of a solution of crystal violet (50 mg/100 ml) in citrate-phosphate-borate buffers of varying pH (Teorell & Stenhagen, 1938). The flasks were equilibrated at 24" (12 h). Samples were removed from each flask and centrifuged at 10 000 rev/min (2 min) and the concentration of crystal violet determined spectrophotometrically at 590 nm. Beer's law was obeyed over the range of concentrations used.Adsorption isotherms of crystal violet on kaolin were determined in the same way at a range of pH values and using crystal violet concentrations ranging from 40-60 mg/100 ml. Equilibration and determination of the dye in the supernatant were carried out as above and the adsorption isotherms constructed. Leaching of inorganic ions front kaolinMeasured amounts of N/100 sodium hydroxide solution were diluted to 100 ml with water, the sodium content measured by flame photometry, kaolin (10 g) was added and the whole allowed to equilibrate overnight. The sodium content of the supernatant was then determined. The experiments were then repeated incorporating EDTA in the mixture and the supernatant assayed for aluminium by complexation with Alizarin S (Barton, 1948) and for magnesium and calcium by atomic absorption spectrophotometry.

The Effect of Bismuth Carbonate and Other Antacids on the Activity of Pepsin

“…One of the conclusions reached was that bismuth carbonate could not be regarded as an antacid because the rise in pH it caused, even when present in excess, was insignificant. These findings have been confirmed by Armstrong and Martin (1953) and Alstead (1941) and (1954). Incidentally, they were also confirmed during the course of the present investigation.…”

Determination and characterization of metronidazole–kaolin interaction

“…The charge will vary with change in pH. The ratio of the surface area edge to face is 1:14 (Armstrong and Clarke, 1971). The structure is electrically neutral but an isomorphous substitution occurs within the lattice and gives rise to a negative charge which is inevitably compensated for by cations being attracted to the surface.…”

Modeling of the adsorption of a protein-fragment on kaolinite with potential antiviral activity

“…Hence, it exhibits two surfaces along the basal plane: siloxane and aluminol (001) surfaces. The charge on these basal planes is predominately polarizable (negative), while the charge on the (110) and (010) edges is pH-dependent amphoteric due to the protonation/deprotonation of hydroxyl groups, where the edges carry a positive charge at low pH and become negative as the pH increases ( Armstrong and Clarke, 1971 ). Recently, kaolinite has been subjected to some useful physical and chemical treatments by modifying its surface and structural properties in a way of enhancing its surface activity and interaction with organics and biomolecules by means of altering charge, porosity and increasing surface area in possible novel active derivatives ( Lagaly, 2006 ; Hu et al, 2013 ).…”