Immobilizing Arsenic and Copper Ions in Manure Using a Nanocomposite

Livestock manure (Man) commonly contains a certain quantity of heavy metal ions, such as arsenic (As) and copper (Cu) ions, resulting in a high risk on soil contamination. To solve this problem, heavy metal of manure was immobilized into sodium carbonate/biosilica/attapulgite composite (Na₂CO₃/BioSi/Attp), which was developed using a nanocomposite consisting of anhydrous sodium carbonate (Na₂CO₃), straw ash-based biochar and biosilica (BioSi), and attapulgite (Attp). When Na₂CO₃/BioSi/Attp was mixed with Man/AsCu, the obtained nanocomposite (Na₂CO₃/BioSi/Attp/Man/AsCu) with a porous nano-network structure could effectively control the release of As and Cu ions from manure through adsorption and chemical reaction. Meanwhile, a pot experiment indicated that Na₂CO₃/BioSi/Attp/Man/AsCu could increase the pH value of acid soil, promote the growth of rice, and significantly decrease the uptake of As and Cu ions by rice. Therefore, this work provides a promising approach to immobilize heavy metal ions in manure and, thus, lower the contamination risk to the environment. Na₂CO₃, BioSi, and Attp powders were mixed evenly with a weight ratio of W_Na/W_BioSi/W_Attp = 3:1:2.