Biochar has good adsorption ability to many kinds of contaminants.In this work,peanut shell,corn cob,cotton stalks and crayfish were pyrolyzed under three temperatures(300℃,450℃,600℃)to obtain biochars for the removal of Ni2+.The biochars were modified with 2 mol/L Na2S solution.Characterization results showed that the specific surface area and total pore volume of modified biochar increased obviously.Among all the adsorbents,the modified corncob biochar(450 ℃)showed the best Ni2+adsorption.The adsorption kinetics followed the Elovich model with an equilibrium time of 24 h.The maximum capacity of the modified biochar could reach 15.40 mg/g.The adsorption process was affected by pH,temperature and coexisting ions.High pH(under pH=7)provided more adsorption sites which enhanced adsorption capacity.Experimental results also indicated that the main adsorption mechanism of Ni2+was ion exchange.Findings from this work suggest that modified biochar can be used as an effective adsorbent for the removal of Ni2+from wastewater.