Synthesis and characterization of clay-based ultrafiltration membranes supported on natural zeolite for removal of heavy metals from wastewater

High cost of high-purity materials is one of the major factors that limit the application of ceramic membranes. Consequently, focus has been shifted to using natural low cost materials such as clay, apatite as alternatives to well-known other metallic oxides like alumina, silica, zirconia and titania. As a contribution to this area, development and evaluation of new but low cost ultrafiltration (UF) ceramic membranes made from nanoparticles of smectite (previously prepared by sol-gel method) are presented in this article. The UF composite membranes were obtained via the Layer-by-Layer technique, and deposited on tubular microporous supports obtained from natural zeolite via the extrusion process. Four different membranes namely; Sm/Z4 (with four layers), Sm/Z5 (with five layers), Sm/Z6 (with six layers) and Sm/Z7 (with seven layers) were prepared. Morphological and textural properties of the membranes (sintered at 900 degrees C for 3 h) were determined by BET and SEM. The measured pore diameters (dp) of the membranes were in the following ranges: 3 nm-13 nm for Sm/Z4; 2 nm-11 nm for Sm/Z5; 3 nm-5 nm for Sm/Z6; and 14 nm-21 nm for Sm/Z7. Heavy metal removal efficiency of these membranes was evaluated using a home-made cross-flow UF pilot plant operated at a temperature of 25 degrees C with trans-membrane pressure (TMP) ranging from 3 bar to 7 bar. Pure water permeability of these membranes varied from 1218 L/h m(2) bar for the ordinary zeolite support (before layer deposition) to 73 L/h m(2) bar; 65 L/h m(2) bar; 59 L/h m(2) bar and 95 L/h m(2) bar for Sm/Z4, Sm/Z5, Sm/Z6 and Sm/Z7, respectively. During the treatment of wastewater (containing heavy metals) obtained from electroplating industry using these membranes, a significant decrease in turbidity (< 1 NTU) was observed and the chemical oxygen demand (COD) removal for Sm/Z6 was > 96%. In addition, the Sm/Z6 membrane displayed heavy metal removal efficiency of >89% for chromium. The overall data suggest that the developed and tested nanocomposite membranes have potential for remediation of industrial effluents contaminated by heavy metals. (C) 2020 Elsevier B.V. All rights reserved.