Quadrupolar study: Aluminium in water

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  • Published: Jul 1, 2016
  • Author: David Bradley
  • Channels: NMR Knowledge Base
thumbnail image: Quadrupolar study: Aluminium in water

Flocculation

This is an analysis using 27Al qNMR (quantitative NMR) spectroscopy. Each spectrum can be measured in just three minutes. Credit: Kobe University

Japanese scientists have reported the first example of fixed-quantity nuclear magnetic resonance (NMR) spectroscopy on the quadrupolar nuclei of aluminium to help them test drinking water.

Maki Hideshi of the Center for Environmental Management at Kobe University, Japan Sakata Genki of the Graduate School of Engineering, Department of Chemical Science and Engineering (currently now employed at Central Glass Co., Ltd.), and Mizuhata Minoru of the Graduate School of Engineering have used aluminium-27 NMR spectroscopy to quickly and accurately measure the concentration of the metal ion that is used to purify tap water. This development could be used in the search for better coagulants for drinking water purification that are more environmentally benign. The team reported its findings to the 76th Japan Society for Analytical Chemistry Symposium.

Rapid detection

Colloidal particulates have to be removed from water in order to provide clear, safe drinking water. This process is usually carried out with the assistance of a polychlorinated aluminium coagulant that binds the nanoscopic and microscopic colloidal particles from raw water and allows them to settle out through sedimentation and then be filtered leaving clear water. Unfortunately, aluminium ions are toxic to fish and can inhibit plant growth as well as representing a wider environmental concern and human health issues. The Japanese Water Works Law specifies that aluminium concentration in water must be kept below 0.1ppm (1 part in 10,000,000) and similar thresholds are in place elsewhere in the world.

The team points out that various hydrolysed species of aluminium ion can be detected in water. However, until now the so-called "ferron method", which involves pigments and absorption meters, has been the detection method of choice used to determine the concentration of these compounds. This analytical method is somewhat sluggish taking several hours to carry out and the results are often erroneous, which is not good for water quality control and environmental protection.

Now, Maki's research group has used optimized NMR equipment to use 27Al qNMR (quantitative NMR) spectroscopy, which enables them to accurately measure the level of each aluminium compound in a water sample. Moreover, the tests take just three minutes or so to acquire the necessary data, which can then be used to determine the concentration of hydrolysed species in the sample with a very small margin of error at all ranges of pH, the team reports.

Agglomeration products

Interestingly, the team has also used the technique to investigate the products of agglomeration and the mechanism by which aluminium ions flocculate colloidal matter from water. They found that when there is a high concentration of aluminium ions in a sample that after approximately 100 minutes a Keggin-type tridecameric cluster (K-Al13 ) is shown to form. After a few months, polymerization occurs.

The team explains that as well as making it easier to measure the concentration of aluminium ions in water, this new analysis method has also clarified the structural changes aluminium ions undergo over time. This, they hope, will allow researchers to develop better, high-performance, flocculating agents that remove colloids from water more efficiently and have a potentially lower environmental impact.

Related Links

Kobe University (PDF in Japanese), 2016: "Analysis of the hydrolysis reaction and coagulation process of aluminum polynuclear complexes using the fixed-quantity 27Al NMR method"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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