Raj P. Singh

Suppressed ion chromatographic analysis of anions in environmental waters containing high salt concentrations

Abstract The literature on the application of suppressed ion chromatography for the analysis of low concentrations of anions in the presence of a high concentration of matrix ions is critically reviewed. It is reported in the literature that suppressed ion chromatographic determinations of anions such as sulfate, arsenate, oxalate, etc., give erroneous results when low concentrations are quantified in the presence of high salt concentrations. In many cases this is believed to arise from overloading of the column by matrix ions, typically by matrix anions. However, as discussed in this review, the erroneous results in the suppressed ion chromatographic determination of small concentrations of anions such as sulfate, oxalate and molybdate in matrices having very high salt concentrations are not caused by column overloading but are due to some anion-proton interactions within the suppressor. Determination of anions of strong acids such as Cl − , Br − , and I − is not affected and they can be accurately quantified by suppressed ion chromatography in aqueous matrices containing high salt concentrations. Suppressed ion chromatography as a tool for the accurate analysis of small concentrations of anions in the presence of high ionic strength matrices, such as subsurface waters, well waters, and aqueous extracts of sandy soils has also been reported.

Ion chromatographic characterization of toxic solutions: analysis and ion chemistry of biological liquids

The literature on the analysis of biological fluids by ion chromatography is reviewed herein. It has been demonstrated that ion chromatography is the method of choice for the determination of anions such as chloride, nitrite, bromide, phosphate, nitrate, sulfate, oxalate, thiocyanate, thiosulfate, citrate, isocitrate, carbonate, and similar species. Cations such as sodium, ammonium, potassium, magnesium, and calcium in various biological solutions have also been successfully identified and quantified. The technique fulfils several requirements of a reliable microanalytical method by providing sufficient speed, automation, case of use, and accuracy. For many types of analyses, very little or even no sample preparation is required. Because of this, as presented in this review, ion chromatography is widely used not only to obtain reliable clinical data, but also to study ion chemistry. It has been an invaluable tool in nephrolithiasis and dental research. This review should provide a useful reference for analysts and researchers involved in clinical studies. The review is presented in four sections: (1) introduction, (2) methods of analysis, (3) ion chemistry and (4) critical comments and concluding remarks. Section 1, as usual, deals with the general introduction of the subject and objectives. Section 2 includes the review of the literature on ion chromatography (IC) methods developed for routine analysis of various analytes present in biological fluids. Section 3 deals with the applications of IC used in the understanding of ion chemistry of biological fluids. Specifically, it deals with the physical chemistry aspects related to nephrolithiasis and dental research, such as speciation, driving force for crystals formation and crystallization, and pathophysiology. Section 4 contains critical comments and concluding remarks.

Characterization and chemistry of formation of a magnesium hydroxide-type scale obtained from the tungsten process

Abstract This paper pertains to the characterization of a scale that forms in the plastic packing of the ammonia-stripping column in the tungsten process. Results indicated that the major phase of the scale contained a Mg(OH) 2 -type structure, which can be represented by Na 2−2 x Mg x (OH) 2− y (WO 4 ) y /2 where 0 x y 2− x (WO 4 ) 1− x (OH) x -type species, which are frequently found to form in concentrated basic sodium tungstate solution. The scale also contained MgWO 4 as a minor phase.

PURIFICATION OF A PHOSPHOROUS-CONTAINING SCHEELITE ORE CONCENTRATE : A DESIGN-OF-EXPERIMENT STUDY

Abstract A “design-of-experiment” (DOE) approach was used to study the purification of a scheelite ore concentrate in HCI. The ore concentrate contained about 65% CaWO4, 18% CaCC3, 14% Ca10(PO4)6(OH)2, and 3% SiO2. In addition to these major phases, the ore concentrate also contained trace amounts of toxic elements such as arsenic, lead, and uranium. These elements were associated with the apatitic part of the ore. The results of DOE experiments indicated that calcite can be selectively removed with a low HCI concentration, and the resulting calcium-containing solution may be used for other applications. Apatite can then be removed with a high concentration of HCI. This solution contains toxic elements such as arsenic, lead, and uranium because of the association of these elements with apatite. High temperature seemed to enhance the dissolution of unwanted tungsten (scheelite part of the ore concentrate), perhaps due to the formation of P- and As-containing heteropoly anions of W, such as PW12O40 3- and A...

Carbonate Precipitation on Sand (α-Quartz)

Many consumer products and specialty chemicals are produced via precipitation and crystallization processes. Typically in chemical industry, precipitation/crystallization processes are involved in the purification and separation of chemicals, development of crystals of specific size and morphology, understanding and the control of unwanted scale deposits, development of coatings, filtration, formation of suspensions, and treatment of process by-products. Several hydrometallurgical processes involve precipitat ion of anions in the purification and recovery of metal compounds.