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R Stanforth

Publications and source records attributed to R Stanforth.

4 recordsLinked to original sources
PubMed2001

Competitive adsorption of phosphate and arsenate on goethite.

The competitive adsorption of phosphate and arsenate on goethite was investigated to better understand the bonding mechanisms for the two ions. The anions were added both simultaneously and sequentially. When added simultaneously, the two ions were adsorbed about equally, with the total surface coverage being slightly greater than for either ion alone. When added sequentially, the extent of exchange for the first ion depended on the equilibration time before the second ion was introduced--the longer the equilibration time the greater the exchange. There is a nonexchangeable fraction for both ions that is approximately equal to the initially adsorbed amount of each ion. The results suggest a two-phase reaction on the surface, with the first phase being a rapid surface complex formation on the goethite surface, followed by the slower buildup of a surface precipitate on the adsorbed layer. The exchangeable ions are in the surface precipitate. These results are incompatible with a surface complexation model (SCM) for anion adsorption on geothite and indicate that the actual reactions are more complicated than the reaction assumed in a SCM.

Adsorption↗
PubMed2000

Integrated hydrometallurgical process for production of zinc from electric arc furnace dust in alkaline medium.

In this study, a novel and integrated hydrometallurgical process for the production of zinc powder from electric arc furnace (EAF) dust in alkaline medium is reported. The dust is firstly hydrolysed in water, and then fused in caustic soda at 350 degrees C for 1h, followed by leaching in alkaline solution in which both zinc and lead are effectively extracted. Zinc powder is then produced by electrowinning from the leach solution after the lead is selectively removed by precipitation using sodium sulphide as precipitant. The EAF dust tested contained 25% Zn, 1.8% Pb and 33% Fe. It was found that 38% of zinc and 68% of lead could be extracted from the dust when leached directly in caustic soda solution. Leaching of zinc increased to 80% when dust was directly fused with caustic soda followed by alkaline leaching. However, the leaching further increased to 95% when the dust was hydrolysed first with water before fusion. Zinc powder with a purity of 99.95% was then produced by electrowinning from the lead depleted solution. Stainless electrodes were used as both anode and cathode.

Dust↗
PubMed2000

Distinguishing Adsorption and Surface Precipitation of Phosphate on Goethite (alpha-FeOOH).

The reaction between phosphate and goethite changes from adsorption into surface precipitation with no discernible changes in the adsorption isotherm. Distinguishing the two processes, by plotting the loss of phosphate from solution versus final phosphate concentration or based on theoretical calculations, is difficult. This paper presents a method for distinguishing between the two processes based on the change in zeta potential with increasing adsorption. During adsorption, the incoming phosphate results in a more negative surface charge as the more acidic phosphate ion replaces a less acidic surface hydroxyl. The amount of negative charge imparted to the surface should vary linearly with surface coverage for adsorption. Phosphate that is bound to a surface precipitate, on the other hand, imparts a much smaller negative charge to the surface, since there is no change in the character of the surface due to the additional phosphate. Zeta potential measurements of phosphated goethite at varying solution pH values and surface coverages are used to determine the transition point from adsorption to surface precipitation. The transition occurs at dissolved phosphate concentrations much lower than those calculated for phosphate in equilibrium with goethite and iron phosphate. Copyright 2000 Academic Press.

Journal Article↗