Roger Dahl

Determination of lanthanides in magnesium alloys by ion chromatography

Abstract A certain amount of lanthanide elements can be added to the magnesium metal alloys in order to improve their mechanical properties and corrosion behaviour. The light fraction La, Ce, Pr and Nd is normally added to the metal during the alloy production process. The determination of these elements in the magnesium alloy is usually carried out by different atomic spectroscopic techniques with the exception of cerium which is difficult to determine by atomic absorption spectroscopy (AAS) due to matrix interference. These techniques include X-ray fluorescence (XRF), optical emission spectroscopy (OES), inductive coupled plasma-mass spectroscopy (ICP-MS) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and AAS. This paper presents an analytical procedure for the determination of these elements in the magnesium alloy by ion chromatography. The determination of La, Ce, Pr, and Nd by cation exchange chromatography, ion interaction chromatography and anion exchange chromatography is also discussed. The accuracy and reproducibility of the cation exchange Chromatographic method are investigated through standardized magnesium alloy materials. A comparison of analytical data was set up to study the suitability of this method against standard methods of analysis like ICP-AES and AAS spectroscopic techniques. It was apparent that data obtained from this work closely matches with data obtained from the two other methods of analysis. This work indicates that the determination of lanthanides in magnesium alloys by ion chromatography is fast, reliable and accurate.

Determination of thorium and uranium in nitrophosphate fertilizer solution by ion chromatography

Different phosphate rocks contain various concentrations of thorium and uranium and the range of these concentrations can be significant. Digestion of phosphate rocks with concentrated nitric acid in a fertilizer production process leads to the dissolution of these metals in the resulting nitrophosphate solution. A direct method with a total analysis time of 10 min is described for the determination of thorium and uranium in nitrophosphate fertilizer solution. The method is based on cation-exchange chromatography coupled with spectrophotometric postcolumn detection with Arsenazo III at 660 nm. Elution is performed with a gradient concentration of hydrochloric acid or nitric acid and ammonium sulphate, utilizing a strong cation-exchange analytical column to perform the separation.

Determination of lanthanides in Kola nitrophosphate solution by cation-exchange ion chromatography

Abstract Lanthanides and yttrium are present in Kola phosphate rock. Digestion of this rock with concentrated nitric acid in the Odda process of fertilizer production leads to the dissolution of these metals in the resulting nitrophosphate solution. This nitrophosphate solution is considered as a complex analytical matrix. In this paper, we present an analytical method with a total analysis time of 18 min for the direct determination of lanthanides and yttrium in the above nitrophosphate solution, based on cation-exchange ion chromatography. The analytical columns involved in this method are silica-based cation exchanges. Elution was carried out with a concentration gradient of HIBA (α-hydroxyisobutyric acid) at a pH range between 3.8 and 4.2, coupled with post-column spectrophotometric detection with PAR or ARSENAZO III at 530 and 658 nm respectively. These silica columns can also offer the direct analysis of lanthanides in organic solutions taken from experimental research samples, investigating the extraction of these metals from the nitrophosphate solution by liquid-liquid extraction.

Determination of total chromium in phosphate rocks by ion chromatography

Chromium(VI) is one of seven elements which is classified in the fertilizer industry as being harmful to plants and biological systems. Phosphate rocks represent the raw material for complex fertilizer production in the world. This paper investigates for the first time the determination of total chromium in phosphate rocks by ion chromatography. The developed analytical method involves the digestion of phosphate rocks with nitric acid followed by sample treatment of the resulting solution. The digestion solution obtained was treated with an oxidising agent (potassium peroxosulphate) to convert all chromium to the hexavalent state. The analytical method developed utilizes anion-exchange ion chromatography to achieve the separation and spectrophotometric post-column reaction for detection with diphenylcarbazide. The relative standard of deviation from analytical data comparison of six different phosphate rocks with atomic absorption spectrometry and inductively coupled plasma atomic emission spectrometry techniques, and cross-analysis data against an internationally certified phosphate rock standard were between 0.58 and 1.45%. Calibration curve between 0.2 and 0.9 microgram/ml was excellent, and the method has a detection limit for Cr(VI) of 0.05 ng. The developed method offers a fast, a reliable and an alternative procedure for the determination of total chromium in phosphate rock deposits by ion chromatography.