Simultaneous Adsorption of Aqueous Pb2+, Cu2+, Zn2+, and Cd2+ Using Surfactant-Modified and Unmodified Activated Carbon in a Fixed Bed Column

The goal of this work is to improve the simultaneous removal of Pb2+, Cu2+, Zn2+, and Cd2+ ions from synthetic wastewater in a fixed bed column by incorporating sodium dodecyl sulfate (SDS) onto the surface of activated carbon made from coconut shells. The activated carbons were characterized using Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy-energy dispersive x-ray (SEM-EDX). The adsorption column dynamics were studied by varying the flow rates (5, 10 and 15 mL/min), bed heights (10, 15 and 20 cm), and initial concentrations (50, 150, and 250 mg/L). The activated carbon has a pore volume of 0.715 cm3/g and a BET-specific surface area of 1410 m2/g. Sodium dodecyl sulfate (SDS) surfactant incorporation onto the surface of the activated carbon enhances its capacity for simultaneous adsorption of Pb2+, Cu2+, Zn2+, and Cd2+ from the aqueous medium. The affinity of the heavy metals to both unmodified (AC) and modified (AC-SDS) activated carbons followed the order of Pb2+ > Cu2+ > Zn2+ > Cd2+. The dynamic adsorption of the column depends on the flow rate, bed height, initial metal concentration, and SDS surface modification. With a 5 mL/min flow rate, a 20 cm bed height, and a 50 mg/L initial metal concentration, a maximum break-through time of 150 minutes for the unmodified activated carbon (AC) and 180 minutes for the SDS-modified activated carbon (AC-SDS) was reached.

Adsorption of humic acid from aqueous solution on bilayer hexadecyltrimethyl ammonium bromide-modified zeolite

Surfactant-modified natural zeolites(SMNZ)with different coverage types were prepared by loading hexadecyltrimethyl ammonium bromide(HTAB)onto the surface of a natural zeolite.The adsorption behavior of humic acid(HA)on SMNZ was investigated.Results indicate that the adsorbent SMNZ exhibited a higher affinity toward HA than the natural zeolite.HA removal efficiency by SMNZ increased with HTAB loading.Coexisting Ca2+in solution favored HA adsorption onto SMNZ.Adsorption capacity decreased with an increasing solution pH.For typical SMNZ with bilayer HTAB coverage,HA adsorption process is well described by a pseudo-second-order kinetic model.The experimental isotherm data fitted well with the Langmuir model.Calculated maximum HA adsorption capacities for SMNZ with bilayer HTAB coverage at pH 5.5 and 7.5 were 63 and 41 mg·g^(-1),respectively.E2/E3(absorbance at 250 nm to that at 365 nm)and E4/E6(absorbance at 465 nm to that at 665 nm)ratios of the residual HA in solution were lower than that of the original HA solution.This indicates that the HA fractions with high polar functional groups,low molecular weight(MW),and aromaticity had a stronger tendency for adsorption onto SMNZ with bilayer HTAB coverage.Results show that HTABmodified natural zeolite is a promising adsorbent for removal of HA from aqueous solution.