Research Highlights

Cashew nut shell mops up heavy metals

doi:10.1038/nindia.2012.25 Published online 22 February 2012

Researchers have produced a novel adsorbent material from chemically modified cashew nut shell, an agricultural waste product. The material is able to remove harmful heavy metals such as copper, cadmium, nickel and zinc from aqueous solutions, and could therefore be used to mop up heavy metals from industrial wastewater.

In their search for a cheap and effective solution, the researchers prepared a new adsorbent by modifying cashew nut shells with sulphuric acid. They made separate solutions of heavy metals by dissolving salts of copper, cadmium, zinc and nickel in double-distilled water. They studied the metal-ion-removal efficiency of the treated cashew nut shells at various temperatures, pH levels and adsorbent quantities, over a range of time periods.

The study revealed that sulphuric-acid-treated cashew nut shell removed the most metal ions from aqueous solution at pH 5. The number of ions removed decreased at lower pH but increased at higher adsorbent doses due to the larger surface area. Maximum ion removal occurred at an adsorbent dose of 1 g l–1 and a temperature of 30 °C.

The removal of metal ions increased with rising contact time, reaching an equilibrium at 30 min for all metal ions. "The sulphuric-acid-treated cashew nut shell has demonstrated an adsorbing capacity that is several hundred times better than bacteria and other natural adsorbents such as barley straw, coir and tea factory waste," says lead researcher Subramanian Sivanesan.

The authors of this work are from: Department of Chemical Engineering, SSN College of Engineering, Chennai, & Department of Chemical Engineering, AC Tech, Anna University-Chennai, India and Department of Chemical Engineering, University of Louisiana at Lafayette, USA.


  1. Kumar, P. S. et al. Adsorption of metal ions onto the chemically modified agricultural waste. Clean-Soil Air Water 40, 188-197 (2012) | Article |