Water pollution because of the presence of heavy metals remains a serious worry. The present work demonstrates the exclusion of cobalt ion (or Co(II)) from water using novel and cost-effective biosorbents. Initially, the biosorbent was chemically modified using orthophosphoric acid and then subjected to calcination to result acid modified date seed biochar (AMDB). Three biosorbents (AMDB400, AMDB500, and AMDB600) were synthesized concerning different activation temperatures (400, 500, and 600 °C). The maximum biosorption of Co(II) was achieved on AMDB600 (149.5 mg/g), followed by AMDB500 (138.33 mg/g), and ADMB400 (129.17 mg/g). For all three biosorbents, the Co(II) removal remained effective within 50-100 min
later it reached saturation. The kinetic analysis suggested strong Co(II) adsorption on AMDB surfaces. The Co(II)-AMDB biosorption data fits well with Temkin isotherm, indicating the heterogeneity on the biosorbent surface and no interaction between adsorbed Co(II)-Co(II) species. The thermodynamic analysis suggested the exothermic and spontaneous adsorption. The intraparticle diffusion of Co(II) within the biosorbent was surface diffusion controlled, as characterized by pore volume and surface diffusion model. The biosorbent reusability was 88.7% after five adsorption-desorption cycles. Thus, presently synthesized biosorbent could be novel and cost-effective for Co(II) and other heavy metal elimination from water bodies.