硫化物全液态电解制备锑及锑-铅合金研究

Antimony （Sb）and lead (Pb) and their alloys are commonly used for batteries and structure materials. The primary ores of Sb and Pb in the crust are sulfides, i.e. Sb2S3 and PbS. The current industrial approaches to extracting Sb and Pb from their minerals involve multiple steps, producing a huge amount of highly toxic and greenhouse gases. Direct electrolysis of a molten sulfide, e.g., molten Sb2S3, is a promising alternative approach but it has a low current efficiency because of its intrinsic semiconductive property allowing the electrons to pass through the electrolyte between anode and cathode. To mitigate the electronic conductivity of the molten sulfide electrolyte, a halide molten salt only conducing ions could be fitted on the top of the molten semiconductor, blocking the electrons transfer through the electrolyte thereby increasing the efficiency. Because the Sb, Pb and their corresponding sulfides have relatively low melting point, and the different densities of molten salt, molten sulfide and liquid Sb and Pb, as well as their immiscibility of each other, a full-liquid “molten salt/molten sulfide/molten metal” three-layer cell can be designed to enable a fast reduction kinetics and self-collection of liquid metal products at the bottom of the electrolysis cell. In this project, we mainly focus on analyzing the thermodynamic properties of electrolyte and electrodes to set a basic guideline for selecting electrodes and electrolytes for electrolysis, investigating the mechanism of electrochemical reduction of molten Sb2S3 and Sb2S3-PbS, and controlling the compositions of electrolytic Sb-Pb alloys. At the end of this project, we aim to reveal the mechanism and rate-limiting step of the electrochemical reduction of liquid Sb2S3 and Sb2S3-PbS, and understand the thermodynamic/kinetic factors governing the formation of alloys, and thereby providing the fundamental knowledge and technology for producing Sb and Sb-Pb alloys by electrolysis of molten sulfides.

金属锑和铅及其合金广泛用于电池及结构材料,它们在地壳中主要以硫化物存在。目前改变了传统工艺的直接电解液态硫化物方法是研究的热点。然而液态金属硫化物是半导体，导致直接电解法电解效率低。针对这个问题，本项目利用高温熔盐离子导体作电解质来阻隔直接电解液态硫化物过程中电子在电解质中的传导，构筑“熔盐/液态硫化物/液态金属”三液层结构，提高电解效率，实现以电解产品的自动收集和加快阴极电还原动力学过程。重点研究：熔盐和电解液态硫化物所需关键材料热力学计算筛选；液态Sb2S3及Sb2S3-PbS还原的电极反应过程； Sb-Pb合金制备的调控机制。项目研究将揭示Sb2S3及Sb2S3-PbS电化学还原机理和限制步骤；明晰它们在电解质中的传质规律，拟解决影响Sb2S3及Sb2S3-PbS电解过程和Sb-Pb合金组成的热/动力学关键问题。项目将为全液态电解硫化物制备锑及锑-铅合金提供理论基础和技术储备。

金属锑（Sb）和铅（Pb）及其合金材料在国民经济发展中占据重要地位，在国防、科技、工农业以及日常生活中都有广泛应用。自然界中的锑、铅多以硫化物矿藏的形式存在，如方铅矿（PbS）、硫锑铅矿（Pb5Sb4S11）、辉锑矿（Sb2S3）、脆硫锑铅矿（Pb4FeSb6S14）等。传统Sb和Pb提炼流程长，并产生大量有害排放。目前改变了传统工艺的直接电解液态硫化物方法是研究的热点。由于金属硫化物多为半导体，使得其电解难度小于一般固相电还原金属氧化物。本项目利用高温熔盐离子导体及强碱性水溶液作电解质来实现电子及阴离子在电解质中的高效传导，构筑“熔盐（或强碱性溶液）/（液态）硫化物/（液态）金属”三相结构，提高电解效率，实现以电解产品的自动收集和加快阴极电还原动力学过程。计算分析了熔盐和强碱性溶液中电解硫化物所需的关键材料热力学；通过循环伏安法分析了Sb2S3及PbS还原在两种体系中的电极反应过程；探索了不同温度、不同电解时间、不同电解体系对Sb、Pb电解产物的影响，总结了对Sb、Pb电解产物形貌的调控性能，并测试了电解产物Sb作为钠离子电池负极材料的电池性能。