###### Contents  
* 1 Introduction
* Water purification and the removal of toxic substances from wastewaters are increasing global challenges. Both surface and ground waters worldwide are reported to be contaminated with impurities deriving from natural and human-involved sources [1]. Metals such as cadmium, chromium, copper, nickel, and zinc (Zn) are commonly associated with pollution problems [2]. Significant anthropogenic sources of Zn in the environment include: metallifreous mining [2]; agricultural sources, such as fertilizers and manure; sewage sludge [3]; metallurgical industries, such as the production of special alloys and steel [4]; landfill leachates [5]; electroplating in the metal finishing industry [6]; and miscellaneous sources, such as batteries [7]. For humans, Zn is an important micronutrient, but too-high amounts of Zn can cause depression, lethargy, and neurologic issues such as seizures and ataxia [8; 9; 10; 11]. Therefore, the effective removal of Zn from water is vital. Various methods and combinations of methods exist for the removal of Zn, including electrocoagulation [7], ion exchange [5], membrane filtration [6], coagulation-flocculation, flotation,and chemical precipitation [8]. The most frequently used methods are ion exchange and membrane filtration [8]. In addition, adsorption is a suitable method for removing heavy metals such as Zn because it is simple, highly efficient, and cost-effective and has regeneration potential [11; 12]. Activated carbon is the most widely applied adsorbent for water purification and is traditionally prepared using, for example, coconut shells or coal as a precursor [13]. The literature contains several studies about the preparation of activated carbon from different agro-based biomass raw materials, such as cherry stones, eucalyptus bark saw dust, bagasse, and peanut husks [14; 15; 16; 17; 18]. The preparation of activated carbon basically consists of two stages, carbonization and activation. Carbonization and activation can be performed in one single reaction or in a two-stage reaction where carbonization and activation are separated in time and space [19]. The carbonization yield (degree of conversion) varies widely as a function of the amount of carbon being removed as CO\({}_{\mathrm{x}}\) or hydrocarbons. The production of activated carbon is typically dominated by a compromise between porosity development and process yield [20]. The typical yield for lignocellulosic materials in the carbonization step is 20 wt%-30 wt% and after the activation step the overall yield is approximately 10 wt% [21]. The pore structure of the carbon after the carbonization step is insufficient, and therefore the activation step is needed. In the activation process, spaces between aromatic sheets are cleared of various carbonaceous compounds and disorganized carbon that might have filled the interstices during carbonization. Carbonized material is converted into a form that contains a large number of randomly distributed pores of various shapes and sizes, giving rise to a product with an extended and extremely high surface area. The carbonized material is further treated using chemical or physical activation to increase the surface area and the porosity [22; 23]. Physical activation is a two-stage process in which the carbonization step is followed by physical activation. Physical activation is typically done between 600 \({}^{\circ}\)C and 900 \({}^{\circ}\)C, the temperature range in which the selective gasification of individual carbon atoms take place. Steam and carbon dioxide are the most commonly used physical activation agents [22]. The loss of sample mass during the activation step occurs due to the combined effect of devolatilization and the loss of fixed carbon that remains after the release of volatiles [20; 21]. The porosity is generated in the slow oxidation process where carbon atoms react with oxygen generating carbon dioxide [21].