Using Chemically Modified Tanzanian Cashew Nut Shell Liquid in Sequestering Pb2+ and Cd2+ from Simulated Contaminated Water

Abstract

Cashew nut shell liquid (CNSL)-based micron-sized polymeric particles (MSPPs) of average particle sizes of
approximately 0.1 µm to 0.4 µm, were prepared by formaldehyde emulsion polycondensation of technical CNSL. The
technical CNSL of 820 centipoise viscosity was used. Surface chemical modifications of MSPPs were carried out to
introduce appropriate functional groups for cation exchange. Through suitable reactions with monochloroacetic acid,
concentrated sulfuric acid, and aminopropyltrimethoxysilane, respectively, carboxylic, sulphonic, and aminopropylsilyl
functional groups were introduced onto MSPPs. Column-packed MSPPs and chemically modified MSPP were
successfully used to exchange lead and cadmium ions in contaminated water. The extent of Pb2+ and Cd2+ exchanged
was analysed by AAS. The amount of Pb2+ and Cd2+ exchanged by the unmodified MSPP was 0.022 mg/g and 0.034 mg
/ g, respectively. The amounts of Pb2+ exchanged by the modified resins were 0.056 mg/g, 0.023 mg / g, and 0.103 mg/g
for the carboxylated, sulfonated and aminopropylsilylated MSPPs, respectively. The amount of Cd2+ exchanged by the
carboxylated, sulfonated and arnimpropylsilylated MSPPs was 0.062 mg/g, 0.093 mg / g, and 0.040 mg/g. The results
suggested improvement in Pb2+ and Cd2+ exchange capacity with chemical modifications of the CNSL based polymer
particles. A strong correlation between Pb2+ and Cd2+ uptake of the polymer particles and the pH of the solution is also
observed. The low values of Pb2+ and Cd2+ exchanges, call for further study to optimise the resins' heavy metal ions
uptake capacity