New method for efficient removal of heavy metals from water

In News: A research team at the Indian Institute of Technology (IIT) Mandi has developed a fibrous membrane filter using a biopolymer-based material that helps to separate out the heavy metals from water samples.

• These membranes contain adsorbents — materials that attract and hold the metals.
• These adsorbents contain a large amount of a biopolymer, Chitosan, derived from crab shells that is mixed with a well-known polymer, Nylon.

Heavy Metals

• ‘Heavy metal’ refers to any metallic chemical element that has a relatively high density, atomic weights, or atomic numbers and is toxic or poisonous at low concentrations.
• Eg. Mercury(Hg), Cadmium(Cd), Arsenic(As), Chromium(Cr), Thallium(Tl), Lead (Pb).
• The problems of arsenic pollution in the Ganga basin are well known in India.
• Major hazardous metals of concern for India in terms of their environmental load and health effects are lead, mercury, chromium, cadmium, copper, and aluminium.
• They are released into the water through anthropogenic activities such as mining, manufacturing, electroplating, electronics, and fertilizer production, among others.

About the Invention

• Earlier Method: Melt Blowing method was normally used to produce the fibres used to make regular cartridge filter-assemblies
• New Method: Solution Blowing:
  • The IIT Mandi researchers have used a process called “solution blowing”.
  • Solution blowing produces fibres that are nanometres in diameter.
  • When the fibres get finer, their surface area increases tremendously, which results in better adsorption of heavy metals.
• Benefits of Solution Blowing Method:
  • Adsorption of Heavy Metal: It has made adsorption more efficient.
    • Normally, absorbent fibres bind to the target metal only at their surface, in their nanofiber membranes.
    • But in new natural polymer infused fibres, the adsorption was seen to happen at the sub-surface scale as well, which translates to higher metal removal efficiency.
    • Eg. almost 302mg of copper ions could be adsorbed by 1g of adsorbent.
  • Eco-Friendly: Solution blowing processes can enable blending of natural polymers like chitosan and lignin with synthetic polymers like Nylon.
    • Using this technique, 40 percent of the nylon was replaced with chitosan, which means 40 percent less fossil-fuel derived, polluting plastics
  • Reusable upto 8 times: The membranes could be reused at least eight times before there was considerable reduction in the efficiency of metal adsorption.
  • Easy recovery of adsorbed Metal: Recovery of the adsorbed metal in a metal-hydroxyl nitrate form was also easy, which is a value-addition to the membrane filter.

Source: DTE