## 4 Conclusions  
The prepared nZVI@ATP considerably enhanced Ni\({}^{2+}\) removal as the loading of nZVI onto ATP effectively reduced nZVI agglomeration. The static adsorption analysis of nZVI@ATP for varying iron-ATP ratios revealed that the highest Ni\({}^{2+}\) removal efficiency (71.93%) was achieved when the iron-ATP ratio was 2:1 and its adsorption capacity was 143.86 mg/g. The quasi-secondary kinetics could better describe the adsorption of Ni\({}^{2+}\) by nZVI@ATP composites, and the fitted equilibrium adsorption amount was obtained. The adsorption of Ni\({}^{2+}\) by nZVI@ATP is mainly divided into three stages: surface diffusion, intra-particle diffusion, and adsorption equilibrium. The rate of adsorption of Ni\({}^{2+}\) by nZVI@ATP is limited by other factors such as surface diffusion and surface adsorption in addition to the main intra-particle diffusion. The removal efficiency of nZVI@ATP for Ni\({}^{2+}\) showed an increasing trend as the initial concentration and dosage increased. For a pH of 2-7, the removal efficiency of nZVI for Ni\({}^{2+}\) first increased and then decreased with the pH, and the highest removal efficiency of nZVI@ATP for Ni\({}^{2+}\) was achieved at a pH of 5. It was shown that nZVI@ATP successfully realized the adsorption of Ni\({}^{2+}\). The removal efficiency of Ni\({}^{2+}\) was 71.93% after 13 h at C\({}_{0}\) = 200 mg/L, an adsorbent dosage of 1.0 g/L, and a pH = 5. The recycling of nZVI@ATP revealed that the material still had a high adsorption capacity for Ni after the first cycle, which gradually decreased with an increasing number of cycles. SEM-EDS, FTIR, XRD, and XPS analyses revealed that the mechanism of Ni\({}^{2+}\) removal by nZVI@ATP involved adsorption, reduction, and precipitation, with the main mechanism being the induced Ni(OH)\({}_{2}\) precipitation on the nZVI@ATP surface.  
All authors contributed to the study conception and design. Material preparation, data collection, and analysis were performed by [PERSON] and [PERSON]. The first draft of the manuscript was written by [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON]. All authors have read and agreed to the published version of the manuscript.  
This research was financially supported by the Natural Science Foundation of Ningxia province (2023 AAC03346); the Gansu Key Research and Development Program--Industrial (22 YF7G7A139); the Innovation Fund Project of Higher Education in Gansu Province (2023A-036); the Industrial Support Program of Education, Department of Gansu Province (2021 CYZC-31); the project of Gansu Province Science and Technology Plan (22 CX3 GA076); the Lanzhou Talent Innovation and Entrepreneurship Project (2021-RC-41); and the Research and Practice Project on Education and Teaching Reform in Ningxia Hui Autonomous Region (bjg2023083).  
Not applicable.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
Author [PERSON] was employed by the company Gansu Hansing Environmental Protection Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.