Preparation Of Modified Activated Carbon And Its Adsorption Of Ni²⁺ From Slightly-polluted Source Water

There is a growing concern about drinking water safety due to the severe water pollution problem and increasingly stringent water quality standards. The incidents of heavy metal pollution unexpected have serious impact on the operation of water supply plant. More attentions have been paid to the nickel due to its carcinogenic and contamination accidents. Active carbon adsorption is of great advantages in simple process and renewable, so it is widely used for removal of Ni2+ from water. However, the adsorption performance of general activated carbon for Ni2+ is poor, it is necessary to change the physical and chemical properties of activated carbon by modification for improving its adsorption properties.In this paper, the Ni2+ in slightly-polluted source water was studied and the activated carbon was used to adsorb Ni2+ due to its safety and non-toxic. The coconut shell activated carbon (CS-AC), the wood activated carbon (W-AC) and the coal activated carbon (C-AC) were modified and the best modification solutions were determined by orthogonal experiments. The surface characteristics of the activated carbon before and after modification were analyzed by Scanning electron microscope, N2 Brunauer-Emmett-Teller adsorption analysis, Fourier transform infrared spectrometry and Boehm titration. The influence of activated carbon dosage, reaction time, pH value and initial concentration on the adsorption of Ni2+ were explored. The adsorption properties of activated carbon before and after modification for Ni2+ in slightly-polluted source water were compared. In addition, the mechanism of adsorption of Ni+ was studied preliminarily through adsorption thermodynamics and kinetics.The results showed that:(1)The CS-AC was modified by HNO3-KOH, the W-AC was modified by H2O2-NaOH and the C-AC was modified by HN03-NaOH.(2) More acidic oxygen-containing functional groups were observed on the surface and the BET surface area and total pore volume decreased slightly with part of the micropores changing into mesopores and macropores and no obvious change in pore size after modification.(3) For CS-AC after modification, with addition of 5.0 g/L and the temperature of 30℃, the removal efficiency after reaction for 1 h was 95.55%, with the Ni2+ concentration decreased from 0.4 mg/L to 0.0178 mg/L, which was below the standard of the Standards for Drinking Water Quality in 2006 (GB5749-2006). While only 74.45% of the Ni2+ were removed by CS-AC before modification under the same conditions. Besides, under the same conditions,75.23% and 95.55% of the Ni2+ were removed by W-AC before and after modification, respectively. And 93.40% and 98.88% of the Ni2+ were removed by C-AC before and after modification, respectively.(4)The kinetic data was well described by the pseudo-second order model and the equilibrium adsorption data fitted better to the Langmuir model. The adsorption process was monolayer adsorption and dominated by chemical adsorption with jointly controlled by external diffusion and internal diffusion processes.Three kinds of modified activated carbon functioned better in adsorbing Ni2+ in slightly-polluted source water than the original activated carbon and it could provide a reference for the removal of Ni2+ in slightly-polluted source water.