Wang Xin, Zhang Yuchao, Zhang Hongli, Wu Xiaolong, Ding Jiaqi, Wang Linling, Chen Jing, Wu Xiaohui, Xiao Jinguang, Wang Lei, Tsang Daniel C W, Crittenden John C
School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China.
School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China; Hunan Engineering Research Center for Resource Recovery and Safe Disposal of Industrial Solid Waste, Hunan Hikee Environmental Technology Co., Ltd., Changsha 410001, China.
J Hazard Mater. 2022 Feb 15;424(Pt C):127575. doi: 10.1016/j.jhazmat.2021.127575. Epub 2021 Oct 24.
The enhancing effect of As(III) oxidation on As stabilization by lime is routinely attributed to the lower solubility of Ca arsenates than Ca arsenites. However, this routine explanation is insufficient for the scenario of As(III) partial oxidation, in which Ca arsenites still predominate As leachability due to the relatively high solubility. In this study, an As-Ca sludge with a high As(III) content (96 g/kg, 55% of the As(tot)) was treated by oxidant-lime to clarify the positive effect of As(III) partial oxidation. Lime alone only reduced As(tot) leaching concentrations from 541 to 4.9 mg/L (4.3 mg/L of As(III) and 0.6 mg/L of As(V)), failing to meet the regulatory limit (2.5 mg/L). After partial oxidation of As(III), lime treatment could further reduce As(III) leaching concentrations from 4.3 to below 1.9 mg/L, whereas As(V) remained stable at about 0.6 mg/L. Qualitative and quantitative analyses based on XRD, SEM-EDS, TG, and thermodynamic modeling suggested that the solubility of newly-formed amorphous Ca arsenites (CaHAsO•xHO) after lime treatment determined the final As(III) leachability. The CaHAsO•xHO formed at lower As(III) contents due to As(III) partial oxidation had lower solubility products and possibly higher crystallinity, resulting in the lower As(III) leachability. This study provides new insights into the role of As(III) partial oxidation in deep decline of As(III) leachability during lime stabilization, guiding the treatment of As-Ca sludge as well as other As(III)-bearing solid wastes.
通常认为，砷（III）氧化对石灰稳定砷的增强作用归因于砷酸钙的溶解度低于亚砷酸钙。然而，对于砷（III）部分氧化的情况，这种常规解释并不充分，在这种情况下，由于亚砷酸钙溶解度相对较高，其在砷的浸出性方面仍占主导地位。在本研究中，采用氧化剂-石灰处理了一种高砷（III）含量（96 g/kg，占总砷的55%）的砷-钙污泥，以阐明砷（III）部分氧化的积极作用。单独使用石灰仅将总砷浸出浓度从541 mg/L降至4.9 mg/L（砷（III）为4.3 mg/L，砷（V）为0.6 mg/L），未达到监管限值（2.5 mg/L）。砷（III）部分氧化后，石灰处理可进一步将砷（III）浸出浓度从4.3 mg/L降至1.9 mg/L以下，而砷（V）则稳定在约0.6 mg/L。基于XRD、SEM-EDS、TG和热力学模型的定性和定量分析表明，石灰处理后新形成的无定形亚砷酸钙（CaHAsO•xH₂O）的溶解度决定了最终的砷（III）浸出性。由于砷（III）部分氧化而在较低砷（III）含量下形成的CaHAsO•xH₂O具有较低的溶度积，可能具有较高的结晶度，从而导致较低的砷（III）浸出性。本研究为砷（III）部分氧化在石灰稳定过程中砷（III）浸出性深度下降中的作用提供了新的见解，为砷-钙污泥以及其他含砷（III）固体废物的处理提供了指导。
