LIUJihao1， LIU Laibao1， ZHANGGaoyin1， zhang Lihua1， DANYong1， ZHAOPeng2， LIUYunxiu2
1.School of Materials and Chemistry， Southwest University of Science and Technology， Mianyang 621000， China；
2.Sichuan Shunying Lithium Material Technology Co.， Ltd.， Meishan 620000， China
Abstract
Objective Cement production is known for its high energy consumption and significant environmental pollution. Reducing cement usage in construction industry is key to minimize pollution. Lithium slag （LS）， a solid waste generated during the extraction of lithium carbonate from spodumene ore through nitric acid pressure leaching， contains 96.9% of alumina and silicon oxide， displaying potential pozzolanic activity. LS can be used as a mineral admixture in cement-based materials to reduce cement consumption. However， the particle size of mineral admixtures affects their pozzolanic activity and the performance of blended cement. This paper studies the effects of LS particle sizes on the pozzolanic activity and the performance and mechanical properties of the blended cement.
Methods After drying LS at （105 ± 2） ℃ for 24 h， LS powders with different particle sizes were prepared through ball milling for 20， 40， 60， 80， 100， and 120 min. The specific surface area of the resulting LS powders was measured， and four samples with distinct particle size distributions were selected for further experiments. These samples were named as LS1， LS2， LS3， and LS4 from smallest to largest particle size. Their particle size distribution and microstructure were analyzed using laser particle size analyzer and scanning electronic microscope （SEM）. P·O 42.5R cement， LS1~LS4， and standard sand were used as the main materials. The water-binder mass ratio was 0.5， the mortar mass ratio was 1：3， and the relative cement mass was 30%. LS with different particle sizes was blended to prepare standard mortar test blocks of 40 mm×40 mm×160 mm. The pure cement paste and LS1~LS4 composite pastes with 30% relative cement mass were named as A0， A1， A2， A3， and A4， respectively. The cement mortar and paste test blocks were cured with specified duration under conditions of （20±2） ℃ and 90% relative humidity， and their compressive strength was measured at 3， 7， 28， 56， and 90 d. The mix ratio of the cement paste was the same as that of the mortar， with the standard sand removed. Based on the mix ratio of cement paste， the effects of different LS particle sizes on the fluidity， setting time， and water requirement for normal consistency were assessed. Hardened cement paste specimens were prepared and cured for 28 and 90 d. The effects of LS on the hydration products and pore structure of the cement with different curing days were tested using X-ray diffraction （XRD）， Fourier transform infrared spectrum （FTIR）， and mercury intrusion porosimetry （MIP）. The hydration heat release rate and hydration heat release of A0， A1~A4 pastes within 72 h were measured using hydration heat analyzer.
Results and Discussion The results showed that as ball milling time increased， LS particle size gradually decreased， exhibiting a more spherical shape. Compared to A0， the water requirement for normal consistency increased by 1.5% for A1 and 3.5% for A4. Fluidity decreased by 16.9% for A1 and 44.6% for A4. The initial setting and final setting times for A1 decreased by 15.5% and 5.3%， respectively， and for A4， these values decreased by 27.4% and 14.3%. Hydration heat test results showed that the addition of LS reduced the heat release rate and cumulative heat release. However， with the decrease in LS particle size， both the heat release rate and the cumulative heat release increased， although the overall hydration reaction rate was lower than that of pure cement paste. The compressive strength of A1~A4 cement mortars was lower than that of A0 in the early stage of hydration （3， 7 d）. At 28 d， the compressive strength of A4 reached 122.6%， with a strength of 52.1 MPa， while other LS samples had lower strengths than A0. Beyond 56 d， the compressive strength of the mortars ranked from highest to lowest was A4， A3， A2， A1， and A0， indicating that smaller LS particle sizes promoted the long-term strength development of cement mortar. XRD analysis showed that the intensity of calcium hydroxide （CH） diffraction peak of A1~A4 was lower than that of A0 at 28 d， and decreased with smaller LS particle sizes. At 90 d of curing， the change in CH diffraction peak intensity was consistent with that observed at 28 d， but the decrease in CH peak intensity was more pronounced， This indicated that the active aluminosilicate in LS underwent a secondary hydration reaction with CH generated by cement hydration reaction， forming more calcium aluminosilicate gel. Also， the smaller the LS particle size， the more CH was consumed， resulting in a greater amount of hydrated calcium silicate gel， which promoted strength development. This trend was consistent with the compressive strength results of the mortar. FTIR and MIP analysis demonstrated that the addition of LS increased the content of calcium aluminosilicate hydrate gel， further optimized the pore structure of the hardened cement paste， and increased the volume fraction of gel pores in the test blocks. These findings confirmed that smaller LS particle sizes effectively promoted the cement hydration reaction and improved the compressive strength of the mortar.
Conclusion In this paper， the effects of nitric acid pressure leaching-extracted lithium slag powder with different particle sizes on its pozzolanic activity and the properties of the blended cement were studied. The study provides valuable insights into the use of LS in sustainable building materials.
Keywords： nitric acid pressure lithium extraction slag powder； particle state；cement； pozzolanic activity
Get Citation: LIU Jihao， LIU Laibao ， ZHANG Gaoyin， et al. Effects of particle state of nitric acid pressure lithium extraction slag powder on cement pozzolanic activity and properties［J］. China Powder Science and Technology，2025，31（4）：1−15.
Received: 2024-06-18.Revised: 2024-09-21,Online: 2025-04-03.
Funding Project: 国家自然科学基金项目， 编号： 52378263、 52178254； 四川省自然科学基金项目，编号： 2024NSFSC0914； 西南科技大学研究生创新基金， 编号： 24ycx2031。
First Author: 刘继浩（2001—），男，硕士生，研究方向为超高性能混凝土。E-mail：3032347065@qq.com。
Corresponding Author: 刘来宝（1978—）， 男， 教授， 博士， 四川省学术与技术带头人后备人选， 博士生导师， 研究方向为固废资源化利用。E-mail：liulaibao@swust.edu.cn。
DOI：10.13732/j.issn.1008-5548.2025.04.017
CLC No: TB44； TQ177.6+2 Type Code: A
Serial No: 1008-5548（2025）04-0001-15
