## 1 Introduction  
Despite the rapid advancement of industrial development and its associated positive aspects, including technological advancements, economic growth, and job opportunities, it has concurrently led to increasingly severe environmental problems, which arise from the discharge of numerous amounts of heavy metal elements into water bodies through electroplating, mining, metallurgy, and other activities [1]. In addition, the impact of human activities, such as agricultural production and domestic waste discharge, further contributes to the abovementioned issues, particularly concerning natural water bodies [2]. Over the past 50 years, the average concentrations of heavy metals (Cd, Pb, Cr, Ni, Al, and Mn) detected in surface freshwater around the world, specifically in Africa, Asia, Europe, and South America, have consistently exceeded the safety limits set by the WHO and US EPA [3; 4; 5]. In the industrial zone of Meghna Ghat in Bangladesh, samples have shown excessive levels of Cr, Cd, Ni, and Pb [6]. Similarly, in Nigeria, Cd, Cr, Mn, Ni, and Pb concentrations in surface freshwater have exceeded the maximum recommended levelsfor drinking water set by WHO [7]. Therefore, addressing the problem of heavy metal pollution, particularly removing heavy metal ions from water bodies, is a major global concern [8]. Ni and its compounds have many industrial and commercial uses. Given their widespread use in aircraft, electroplating, steel, and metallurgical industries, excessive Ni content is released into the environment. The Ni\({}^{2+}\) concentrations in terrestrial and aquatic resources can reach 26 g/kg and 0.2 mg/L, respectively, which is about 25 times that of uncontaminated resources [9]. Ni has become one of the major pollutants in the ecological environment. Ni\({}^{2+}\) has detrimental effects on the environment, human body, and microorganisms, and animal experimentations have confirmed the carcinogenicity of Ni compounds as they can induce tumor production and disrupt the human immune system, causing allergic reactions [10; 11]. Currently, compared to the inefficiency of chemical precipitation techniques and the interference susceptibility of ion exchange technologies in the treatment of heavy metall-polluted wastewater, as well as the high cost associated with electrochemical techniques, adsorption presents significant advantages in practicality, cost-effectiveness, and efficiency, making it an effective method for treating Ni. Adsorption is considered to be an efficient, convenient, and economical method for wastewater treatment. The flexibility in design and operation, the high removal efficiency, and the possibility of regeneration and reuse of most adsorbents through appropriate desorption processes contribute to the increasing popularity of adsorption processes. It relies on the interaction between porous solid adsorbents and heavy metal ions, with the main mechanisms including electrostatic adsorption, composite adsorption, ion exchange, etc. [12; 13; 14]. This process promotes the enrichment of heavy metal ions on the adsorbent, ultimately achieving the purpose of purifying the water body [15]. Recently, clay minerals have been widely used as adsorbents for removing heavy metal ions from water [16]. Attapulgeite (ATP), whose theoretical chemical formula is Mg\({}_{5}\cdot\)Si\({}_{8}\cdot\)O\({}_{20}\)(OH)\({}_{2}\)(OH)\({}_{4}\cdot\)4H\({}_{2}\)O, is a 2:1 layered chain hydrated magnesium-rich silicate clay mineral with a specific rod-like crystal structure, considerable surface area, and unique surface charge distribution characteristics [17]. Owing to its rich mineral resources, easy access, low cost, nontoxic nature, and multiple applications, natural ATP has excellent potential for solving heavy metal pollution in water [18; 19]. The ATP clay resources in Linze, Gansu are relatively abundant, with ATP from the Linze mine exhibiting a stratified distribution and a brick-red surface [20].