Environmental impact and management of phosphogypsum

The production of phosphoric acid from natural phosphate rock by the wet process gives rise to an industrial by-product called phosphogypsum (PG). About 5 tons of PG are generated per ton of phosphoric acid production, and worldwide PG generation is estimated to be around 100–280 Mt per year. This by-product is mostly disposed of without any treatment, usually by dumping in large stockpiles. These are generally located in coastal areas close to phosphoric acid plants, where they occupy large land areas and cause serious environmental damage. PG is mainly composed of gypsum but also contains a high level of impurities such as phosphates, fluorides and sulphates, naturally occurring radionuclides, heavy metals, and other trace elements. All of this adds up to a negative environmental impact and many restrictions on PG applications. Up to 15% of world PG production is used to make building materials, as a soil amendment and as a set controller in the manufacture of Portland cement; uses that have been banned in most countries. The USEPA has classified PG as a “Technologically Enhanced Naturally Occurring Radioactive Material” (TENORM).     

The effect of oxygen addition on the determination of cadmium and lead in blood and foods by graphite furnace atomic absorption spectrometry

It is well known that in the analysis of low temperature vaporized metal elements such as cadmium and lead, a high ashing temperature causes a loss of the target atoms at the ashing stage, while low ashing temperature causes incomplete decomposition of organic components in the sample. In order to solve these problems, the effect of oxygen addition on determination of cadmium and lead in blood and foods was studied. Oxygen was introduced into the atmosphere in the graphite furnace at the beginning of ashing stage for 20 seconds at 0.5 l/min. Relation between ashing temperature and sensitivity was examined, and the oxygen addition minimized signal depression by the sample matrix. It can be concluded that the addition of oxygen at the ashing stage not only reduces the background absorption, but also suppress the volatilization of target atoms at the ashing stage by the formation of their oxides.     

Prenatal diagnosis of fragile x syndrome: (cgg)n expansion and methylation of chorionic villus samples

Fragile X syndrome is the most common form of inherited mental retardation, due to an expansion of the (CGG)_n trinucleotide repeat in the FMR-1 gene and hypermethylation of its 5′ upstream CpG island. Two major problems remain to be resolved for fragile X prenatal diagnosis: the abnormal methylation patterns of chorionic villus samples (CVS) and the inability to predict the mental status of females with the full mutation. We present here the results of ten prenatal diagnoses of fragile X syndrome using Southern blotting and polymerase chain reaction (PCR) amplification, and the analysis of 50 further CVS to test the methylation status of the CpG island of the FMR-1 gene. In the ten ‘at-risk’ CVS, eight normal (five males and three females) and two affected male fetuses were detected. Absence of methylation in the CVS was observed in two cases, which was not found upon subsequent examination of the newborn or of fetal tissues. In the 50 CVS not ‘at risk’ for fragile X syndrome, abnormal fragment patterns for probe StB12.3 were detected in 32 per cent for female and 24 per cent for male fetuses. This abnormal pattern could be due to absent or partial methylation of the CpG island of the FMR-1 gene in chorionic villus tissues.     

Removal of tetrafluoroborate ion from aqueous solution using magnesium-aluminum oxide produced by the thermal decomposition of a hydrotalcite-like compound

Magnesium-aluminum oxide (Mg-Al oxide) prepared by the thermal decomposition of a hydrotalcite-like compound was found to have potential for treating NaBF(4) wastewater. The Mg-Al oxide removed the BF(4)(-) and F(-) and H(3)BO(3) from the NaBF(4) solution. With increasing Mg-Al oxide quantity and time, the BF(4)(-) concentration decreased and the degree of BF(4)(-), F(-), and boron removal increased. The decrease in the BF(4)(-) concentration resulted from uptake by the Mg-Al oxide and not hydrolysis. The Mg-Al oxide took up F(-) from the solution preferentially. The Mg-Al oxide also converted the H(3)BO(3) in the aqueous solution into H(2)BO(3)(-), which it took up.     

Electrochemical reduction in vat dyeing: greener chemistry replaces traditional processes

In application of vat dyes the substitution of non-regenerable reducing agents such as Na₂S₂O₄ by cathodically regenerable reducing agents offers great ecological advantages. In a demonstration project a 45 A multi-cathode electrolyser successfully was coupled to a dyeing apparatus for package dyeing with a capacity of 1–10 kg material. Iron-complexes with triethanolamine and Na-d-gluconate were used as cathodically regenerable reducing agents. Dyebath regeneration was performed by ultrafiltration. Substantial reduction in chemical consumption and reduction in wastewater volume, released from the dyeing process could be demonstrated. Quality of dyeings was assessed with regard to levelness and iron content analysed in the dyed samples.