Nanofiltration – Removing Metal Ions from Water by Reverse Osmosis

By AZoM.com Staff Writers

Table of Content

Introduction
Uses of NF Systems
Spiral and Tubular Membranes
Pre-purification of Feeding Water
Benefits of Nanofiltration
Applications of SiC Nano Filters
Other Applications of SiC Nano Filters
Conclusion
About Nanoshel

Introduction

Nanofiltration (NF) is a unique technique that is primarily employed for removing monovalent ions, such as heavy metals, as well as bivalent ions. This method can be depicted as a coarse reversed osmosis (RO); since this technique employs less fine membranes, the feed pressure of the NF system is usually lower in contrast to RO systems. Moreover, the fouling rate is also lower when compared to the RO systems.

Uses of NF Systems

Figure 1. Nano filtration technique

Some of the applications of the NF system are removal of heavy metals from process streams for reuse of water (Figure 1), softening, and reduction of salt contents of slightly brackish water. Standard membrane performance for NF membranes is 90% or more for CaSO4 and 50% for NaCl.

Spiral and Tubular Membranes

Two types of membranes are available such as spiral membranes and tubular/ straw membranes. The former membrane is cost-effective but more susceptible to pollution, while the latter is widely used and is not easily polluted. However, spiral membranes have the largest surface area and hence cheaper to use, while the surface area of tubular or straw membranes is generally less.

Pre-purification of Feeding Water

Pre-purification of feeding water affects the performance of the installation. The requirement of pre purifying depends on the quality of the feeding water. Pre cleaning offers a number of benefits, such as extended life, simple and effective management, and possibility of long production of the installation. In addition, chemical doses can take place to eliminate scaling and precipitation on the surface of the membrane.

Benefits of Nanofiltration

Silicon carbide (SiC) is an innovative nano filter, which has excellent mechanical and chemical properties. It is chemically inert, thermally resistant up to 800°C, and completely stable in solvents. The nano filter (Figure 2) has the highest flux for any filtering material and can accept any amount of oxides. It is also hard, durable, and includes hydrophilic characteristics.

Figure 2. SiC nano filter

Other benefits of this SiC nano filters are rapid and efficient chemical cleaning, excellent performance in water and oil separation, reduced foot print and system costs, and less down time and maintenance.

Applications of SiC Nano Filters

Since SiC has special hydrophilic properties, one can achieve higher water fluxes with SiC- based nano filter when compared to ceramic or polymeric filtering materials. The SiC nano filter also provides option for treating liquids at high temperature and pH.

This is because SiC nano filters are not attacked by chemicals, which are usually found in the industry. These nano filters can be utilized in the full pH-range at any temperature, and thus enable treatment of strong bases and mineral acids.

They can also withstand oxidizers like hypochlorite at any temperature and concentration. Besides treating solutions at severe conditions, SiC nano filters can also be cleaned at harsh conditions.

Additionally, SiC nano filters can be used for waste water re-use application since they exhibit a high mechanical strength, and can be cleaned with strong oxidizers or any chemicals. The nano filters are especially useful for removing manganese and iron in oxidized form with a very high flux.

Other Applications of SiC Nano Filters

The quality of pre-filtration depends on the performance of a RO system (Figure 3). In other words, when suspended solids are removed efficiently, it extends the operating intervals of the RO system prior to the need for chemical cleaning. When the number of chemical cleaning cycles reduces, it prolongs the life of the RO membranes, thus reducing operating costs.

Figure 3. RO system

In addition, efficient removal of suspended solids promotes reduced fouling of the RO membranes. This in turn brings down concentration polarization and enhances the quality of the RO permeate.

In case of pre-filtration for chillers, the efficiency and performance of chillers are directly related to their ability to transfer heat. However, the efficiency of chillers reduces when tubes become fouled. This is because contaminants like mud, sludge, algae, etc. collect on the waterside of heat-transfer surfaces.

However, with the help of SiC nano filters suspended solids can be effectively removed, thus resulting in reduced fouling of waterside of heat- transfer surfaces and chillers tubes. Here, temperature resistance provides a major benefit and helps ensure efficient cleaning at extreme temperatures.

Conclusion

The article clearly demonstrates the benefits of using nanofiltration technique in various applications, such as purification of drinking water, pre-filtration for reverse osmosis, and treatment of waste water.

About Nanoshel

NANOSHEL makes more than 50 types of products, among which the main products are nanotubes, SWCNT's, MWCNT's, and nanoparticles. These products are widely used in the fields such as textile industry, ceramics, chemical fiber, plastics, coatings, cosmetics, rubber, electrical and electronic equipments, electric power generation and boiler and so on.

Through providing the customers with nanomaterials and the application process solution, the company commits itself to assist clients to improve the functionality and technology content of the products so that the clients can promote their product added-values and market competitive competencies, keep their creative advantages for a long time in the concerned fields and make good economic benefits.

This information has been sourced, reviewed and adapted from materials provided by Nanoshel.

For more information on this source, please visit Nanoshel.

Date Added: Oct 23, 2013 | Updated: Oct 23, 2013
Ask A Question

Do you have a question you'd like to ask regarding this article?

Leave your feedback
Submit