## 1 Introduction  
A current environmental issue is the pollution of water resources which occurs mostly due to the disposal of contaminated industrial wastewater [1]. The existence of contaminant compounds in water, especially drinking water, is of considerable risk to the environment and consumers [2]. Among the toxic metals currently found in industrial wastewaters, nickel is one of the most common [3]. According to Decree-Law No. 236/98 of 1 August of the Ministry of Environment, the maximum limit value for the discharge of wastewater containing nickel is 2.0 mg/L [4]. Various industries such as mineral processing, electroplating and production of paints and batteries employ nickel in their activities [5]. Several negative effects may occur when people are exposed to a high concentration of nickel, which means the polluted environment also affects human health. Heavy metals are one of the most dangerous pollutants. When in aquatic environments, even in low concentrations, they represent a risk to the ecosystem sustainability [1]. The use of nickel in several materials used in our daily life contributes to a greater contact with this metal. The most common effect produced by direct contact with nickel is dermatitis, being one of the main precursors of allergic contact dermatitis [6]. Carbonylis the compound of nickel most toxic to humans [7]. The ingestion of nickel can cause inhibition of enzyme activities, damage to the lungs and kidneys, gastrointestinal disease and respiratory problems [8]. Adsorption methods have been attracting significant interest during recent years [9]. The treatment of heavy metals in wastewater using adsorption is making progress through research focused on the development of highly efficient materials, with low cost as well as eco-friendly adsorbents [10]. Alternative materials such as byproducts of agricultural processes have been evaluated due to their efficiency, availability and accessibility [11]. There are many potential biosorbent materials that have been tested to determinate their application in adsorption processes. These materials should have, among other characteristics, high surface area, selectivity, sorption capacity and compatibility with the contaminant and the process [12]. Agricultural biomass residues generally consist of cellulose, lignin, hemicelluloses and proteins which make them successful adsorbents to remove heavy metals [13]. Some studies presented good results by using different biomasses in the decontamination of aquatic environments, and potential biosorbents were discovered. Activated carbons produced by cassava peel, which was applied to remove dyes and metal ions from aqueous solution at various pHs, with adsorption rates from 5.30 to 100%, is one example [14]. Residues from _Jatropha curcas_ were used as biosorbent for the removal of Remazol Brilliant Blue R; the highest removal rate was around 95% at pH 3.0 [15]. _Pinus eliotti_ bark was tested as adsorbent to remove heavy metals such as cadmium, lead and chromium; the uptake was around 90% for all metals tested at pH 5.0 and 7.0 [16]. Heat-treated wood (powdered pine wood) was employed as chromium adsorbent, and the maximum retention was 15.6 to 19.4 mg g\({}^{-1}\) at pH 3 [17]. Activated carbon is the most used adsorbent due to its high specific surface area which can reach almost 2000 m\({}^{2}\)g\({}^{-1}\) as reported before [18; 19]. Several authors reported the specific surface area of different lignocellulosic materials such as coconut dregs residue with 0.38 m\({}^{2}\)/g [20], husks of water bamboo (_Zizania caluciflora_ Turcz. ), with surface area of 1.87 m\({}^{2}\)/g [21], chestnut shell with 7.01 m\({}^{2}\)/g [22] or _Cryptomeria japonica_ wood with 90-145 m\({}^{2}\)/g [23]. Nevertheless, even though lignocellulosic materials have a much lower specific surface area, they are much cheaper and can be discharged after use.