Environmental

Particle size analysis, rheology and the study of zeta potential are important in a variety of environmental applications.

Soils and sediments

Soils and sediments are an important category of materials in the field of particle size analysis. Particle size is important as it determines many aspects of the strength and stability of a soil and properties related to transport and retention of water, heat and nutrients. In the case of sediments it may well give important information about the origin and distribution of material through the action of tidal, wind and other flows. Often the examination of the size of pollen granules present in the sediment can provide important information about a site (such as what types of plant life were present many years ago).

Although characteristics vary depending on origin and method of collection, it is generally true that a typical sample covers a wide size range and may contain material of all sizes. This may range from the submicron area (clays), silt (2-63 microns), sand (63-2000 microns), gravel (2-63 mm), bouldery gravel (63–200 mm) and boulders (anything larger). For such samples the method of sampling is paramount. To get a representative soil sample it should be divided on a spinning riffler into enough material needed for a single measurement. This will greatly increase sample to sample reproducibility.

Modern laser light scattering offers many advantages over traditional sedimentation and hydrometry analyses performed on soils; sample volumes required are low, the analysis is rapid and reproducible and modern instruments such as the Mastersizer family offer a choice of sample presentation techniques. The sample can be analyzed either wet or dry.
Materials where sub 10-micron particles are present have greater van der Waals forces (in ratio to the particle size) compared with larger material. This makes it appear stickier and harder to disperse. Wet dispersion will work better than dry dispersion for such materials.

Dry presentation is suitable for a freely flowing soil that requires little additional dispersing action. Such a sample is likely to be soil from a desert region. Any trace of water present will prevent analysis by dry dispersion. Most fresh soils are measured wet for this reason. Fresh soil will nearly always contain material with material outside the measurement range of the instrument, so a sieve is used to take a "top cut" of the sample.

Soil scientists often use a different size classification to present data. This is known as "phi notation" and is passed on a power of 2 series where the class boundaries are labeled by the index. In this notation the Mastersizer 2000 measures from 15.5 phi (21 nm) to –1 phi (2000µm). Phi tables and graphs are provided in the Malvern software.

Water Treatment

The Zetasizer Nano Z is an important tool in the water treatment industry. While many applications require a high charge on the particles to ensure stability, in the water industry the aim is to reduce the zeta potential of the suspended particles close to zero to cause them to flocculate. In order to do this various chemicals are added, such as Aluminium salts and polyelectrolytes. As these materials are a significant part of the cost of treatment, measurement of the zeta potential can be used to reduce the dosage required and significantly lower operating costs. In addition, with better control of flocculation, using fewer additives, filter run time can be increased.

The MPT-2 autotitrator can be added to the Zetasizer Nano Z to automate the determination of the optimum dose required to reduce the zeta potential to the target value.

Since these materials are pumped at varying pressures and in a wide variety of pipe diameters, knowing the fluid mechanical properties is very important. Malvern rheometers are routinely used for determining the viscosity and fluid properties over a wide range of shear and temperature, enabling critical measurements of pressure drop to be used to assist in pipe design and for minimizing pump start up problems.