Removal of anionic and cationic pollutants from aqueous solutions by using activated carbon prepared from apricot, peach stones and almond shell mixture

During the storage and use of wastewaters caused by different types of industries, result of leakage occurring groundwater is encountered heavy metal pollution. Nickel and chromium are common heavy metals found in these contaminated ground waters. Both of these heavy metals are both toxic and carcinogenic. Therefore, the wastewaters containing heavy metals such as Cr(VI), Ni(II) requires effective treatment by suitable techniques before discharging into aquatic environments and their concentrations must be reduced below the permissible limit. Various treatment technologies such as ion exchange, reverse osmosis, chemical precipitation, membrane filtration, solvent extraction and adsorption have been developed for the removal of heavy metal from water/waste waters. Compared with other methods, adsorption is accepted as the most effective and widely used method for the removal of heavy metal ions due to its high adsorption capacity, easy use, low operating cost and environmentally friendly nature features. The adsorption performance of the fixed bed columns is described through the concept of the breakthrough curve obtained from column experiments. The shape of the breakthrough curve and the time of appearance of the breakpoint are very important characteristics for determining the operation and dynamic response of an adsorption column. In this work, an activated carbon prepared previously from a mixture of apricot and peach stone shells and almond shell was used for the removal of Ni(II) and Cr(VI) from aqueous solutions in a fixed-bed column. The influence of several operating parameters, such as flow rate, pH value, initial metal concentration, adsorbent bed height and temperature on the fixed-bed adsorption process were investigated and three different kinetic models such as the Adams-Bohart, Thomas and Yoon-Nelson were used to determine the kinetic parameters and to analyze the breakthrough curves in the adsorption process. The removal of Ni(II) metal was studied in the first step of the column experiments. Two experimental results showed that the adsorption capacity of active carbon used for Ni(II) removal was low. Therefore, other parameters have not been studied. In the second step, experiments were carried out for the removal of Cr(VI). The adsorption capacity was increased with an increase of the bed height and influent Cr(VI) concentration, but decreased with the increasing the flow rate, pH and operating temperature. The adsorption capacity of Cr(VI) onto AC was also strongly dependent on the solution pH. The results obtained indicate that Thomas model is more suitable dynamic model to full description of breakthrough while the Adams–Bohart model is only advantageous for the initial region of breakthrough curves (i.e., when Ct/C0 < 0.5). The results show that the active carbon prepared from the triple mixture can not be adsorb positively charged cationic Ni(II) ions from aqueous solutions but can be used as an effective and environmentally friendly adsorbent for the removal of Cr(VI) ions in anionic form. Key Words: Ni(II) and Cr(VI), Adsorption; Activated Carbon, Fixed-Bed Column