Pumping Zinc Oxide
Zinc oxide is a white, solid and odourless powder with a bright, almost luminescent appearance.
It is poorly soluble in water although highly soluble in acids and bases. As a chemical it is toxic when vaporised or when present as a fine dust in the air.
Zinc oxide can not be pumped in its natural state, it must be first put into solution. This may be in acids, liquid polymer, food stuffs or pharmaceutical/cosmetic slurry.
The electrical and mechanical properties include it in applications such as LCD screens and ceramics.
- Zinc oxide is an important ingredient in ceramic glaze where it can be used to produce brilliant, glossy finishes and also in products to protect against electrical surges.
- In the manufacture of rubbers and plastics, zinc oxide is used as part of the vulcanization process and for adding strength and integrity to blends.
- As an anti-bacterial measure, zinc oxide can be added to many products including food packaging, medical creams and paints.
- With its photo-refractive quality, zinc oxide may be used as an ingredient in sunscreen, white paint and coatings for windows and paper.
The addition of zinc oxide powder into solution requires a pump which can handle abrasive material, potentially high viscosity or highly corrosive slurry.
Where zinc oxide is being dosed into a mix, a peristaltic pump can provide a solution for accurate delivery and resistance to the abrasive effect of the slurry. The pump contains the media within a hose inside the pump casing. This hose is then compressed along its length by a rotor, drawing and pushing it through at a constant rate. This has several benefits, namely no abrasive wear on any moving parts, zero contamination of the fluid and the accurate delivery rate, which can be crucial in the quality control of a batch. A peristaltic pump also has the advantage of being able to handle high viscosity and higher S.G., making it ideal for pigment solution.
In ceramic production, particularly where compressed air may be in use such as in ATEX rated zones, an air operated double diaphragm (AODD) pump may be more suitable. Where zinc oxide is being handled as part of a ceramic glaze, the need for a pump which can handle the abrasive and corrosive fluid is met by an AODD pump.
Principally this is thanks to the pump having a wide range of materials which are both resistant to wear and corrosion from strong chemicals.
The material selection is determined by the solvent or carrier fluid for the zinc oxide and the temperature.
Elastomers incude Geolast which is highly resistant to abrasion. A cast iron body is preferable where the carrier fluid allows. Should the slurry be corrosive, the operator may have no other choice to accept
PTFE which although is resistant to chemicals will suffer more from abrasion and require replacing regularly. A stainless steel body may also be required and in extremely hazardous environments an all-PTFE AODD pump.
Both the AODD and peristaltic pumps can run-dry and selfprime, so they are very robust to day-to-day operation. Where higher pressures, flow rates and viscosities are present, a progressing cavity pump may be more suitable. The working principle of the positive displacement rotor and stator can provide very reliable performance with a smooth, non-pulsating, consistent flow, making it ideal for dosing.
Progressing cavity pumps are also available with wide feed hoppers for highly viscous fluids such as mashes, doughs and fibrous mixes found in the paper industry.