Zeolite hollow fibre membrane for nickel removal

Abstract

This work was aimed to develop the zeolite hollow fibre adsorptive membrane and also examine the feasibility test of composite zeolite hollow fibre membranes, with UV-curable resin (UCR) as a secondary coating material for the removal of Ni(II). The preparation of the membrane began with the preparation of a alumina hollow fibre membrane as a support. After that, the zeolite crystals being deposited on the outer surface of alumina support using two different techniques namely in-situ crystallization and secondary growth method. The X-ray diffraction analysis (XRD) and morphological study using field emission-scanning electron microscopy (FESEM) shown the zeolites were well crystallized on alumina support for both methods. The membranes performance in Ni(II) removal were tested using batch adsorption study with both preparation methods shows a slightly different in adsorption capacity. Under optimum condition, the S5 membrane prepared using secondary growth method showed a slightly high adsorption capacity of 126.2 mg g-1 with 63% of nickel ions removal from aqueous solution within 180 min of contact time. However due to a slightly performance different, the in-situ crystallization method has been selected as a preparation method for zeolite membrane throughout the current studies because this preparation method is simpler. Parameters affecting the growth of zeolite layer on alumina support were also studied to obtain the most efficient membrane. The concentration of zeolite, the time of crystallisation and the number of zeolite coating layers affect the morphological characteristics of the zeolite membrane. In order to increase the stability of zeolite layer on the surface of alumina support, a photopolymerization process has been done. The addition UCR layer on the outer surface of zeolite membranes have preserved the zeolite particles being detached from the alumina support. The addition of UCR layer also has increased the hydrophobicity as the zeolite membranes itself were exceptionally hydrophilic. The hydrophobicity of the membrane was determined using water contact angle measurement. PMDL membrane gave the highest contact angle value (117.75°) which means that this membrane is very hydrophobic. The performance of zeolite membranes were tested for forward osmosis (FO) process with the most efficient membranes were applied for the removal of Ni(II) from aqueous solution. Filtration test proved that the zeolite membrane enabled to reduce the concentration of heavy metal at ppb level. For the FO process, the result shows that MSL3 membranes enabled a reduction of reverse solute once incorporated with UCR. The lowest reverse solute flux obtained was 0.008 kg m-2 h-1. However, the UCR was unstable in the presence of Ni(II), which later formed complex ions. Adsorption of Ni(II) ions has caused an agglomeration of zeolite particles, causing membrane defects. The present work has successfully developed an alternative zeolite membrane for the removal of heavy metals from water sample.