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Comparative Optimization of Binder Proportions for Cadmium-Contaminated Soil Using Orthogonal Experiments and Response Surface Methodology: Stabilization Mechanisms
QIN Na, TIAN Bin, ZHANG Xiao-peng, LIN Xiao-ming, TANG Zheng
Journal of Changjiang River Scientific Research Institute ›› 2026, Vol. 43 ›› Issue (8) : 130-139.
PDF(9255 KB)
PDF(9255 KB)
Comparative Optimization of Binder Proportions for Cadmium-Contaminated Soil Using Orthogonal Experiments and Response Surface Methodology: Stabilization Mechanisms
[Objective] The primary objective of this research is to develop and optimize a novel, sustainable, and cost-effective binder for the stabilization/solidification (S/S) treatment of cadmium (Cd)-contaminated soils by utilizing a multi-component system comprising red mud (RM), granulated ground blast furnace slag (GGBS), carbide lime residue (CCR), and phosphogypsum (PG), all of which are industrial waste materials. A secondary objective is to compare the effectiveness of response surface methodology (RSM) with traditional orthogonal experimental design (OED) in optimizing the binder composition for achieving both high unconfined compressive strength (UCS) and low Cd leaching concentrations. The study also aims to elucidate the mechanisms governing Cd stabilization within the treated soil matrix via advanced microstructural characterization. [Methods] Artificially Cd-contaminated soil was prepared and treated with varying proportions of the RM-GGBS-CCR-PG binder. Two parallel optimization approaches were used: (1) OED (L9 (34) orthogonal array) to identify the key factors affecting the S/S performance and (2) RSM (Box-Behnken design) to model the complex relationships between binder components (CCR, PG content, and RM/GGBS ratio) and responses (UCS and Cd leaching). Following curing, the treated soil samples were subjected to UCS testing and leaching tests. The experimental data obtained from RSM were used to develop quadratic polynomial models, perform analysis of variance (ANOVA), and generate response surface plots. The optimal binder composition was determined by maximizing UCS and minimizing Cd leaching. X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), was performed to identify the reaction products and elucidate the Cd stabilization mechanisms. [Results] The RM-GGBS-CCR-PG binder effectively stabilized Cd in the contaminated soil. Both OED and RSM identified the RM/GGBS ratio as the most significant factor influencing both UCS and Cd leaching. RSM provided a more refined optimization, leading to a binder composition of 13.77% CCR, 10% PG, and a RM/GGBS ratio of 0.57∶1. At this optimal composition, the treated soil achieved a UCS of 2.12 MPa and a Cd leaching concentration of 1.57 mg/L. ANOVA results for the RSM models showed that the models were highly significant (p<0.000 1) and exhibited a good fit (R2>0.99). XRD analysis revealed the formation of hydration products such as C-(A)-S-H, ettringite (AFt), and Cd-containing precipitates (Cd(OH)2, CdCO3, Cd3(PO4)2). SEM-EDS confirmed the encapsulation of Cd within the C-(A)-S-H gel matrix and the formation of Cd-bearing precipitates. Replacing 1 kg PC with 1 kg of the waste-based binder lowered CO2 emissions by 0.81 kg, embodied energy by 3.93 MJ, and natural resource consumption by 1.73 kg. At a 10% dosage, material cost for S/S was approximately 24.7 CNY/m3 for the RM-GGBS-CCR-PG system versus approximately 99.95 CNY/m3 for PC—an approximately 75% reduction—reflecting the low processing burden of industrial by-products (with GGBS requiring only modest grinding) relative to clinkerized binders. Therefore, the optimized mix simultaneously advanced mechanical performance, contaminant immobilization, and environmental-economic metrics. [Conclusion] This study demonstrates the feasibility of utilizing a novel multi-component binder composed entirely of industrial waste materials (RM, GGBS, CCR, and PG) for the effective stabilization/solidification of Cd-contaminated soils. The RM-GGBS-CCR-PG binder exhibits superior performance compared to Portland cement in terms of both mechanical strength and Cd immobilization. The application of response surface methodology (RSM) proves to be a powerful tool for optimizing the binder composition, providing a more precise solution than the traditional orthogonal experimental design. The study elucidates the mechanisms of Cd stabilization, highlighting the roles of physical encapsulation, chemical precipitation, ion exchange, and surface complexation. Furthermore, the carbon footprint and cost analysis demonstrate the substantial environmental and economic benefits associated with the use of this waste-based binder.
industrial solid waste / cadmium-contaminated soil / orthogonal experiment / response surface methodology / solidification/stabilization
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Heavy metal pollution is a nefarious issue with implications for life. Heavy metals are natural occurring elements, having both natural and anthropogenic sources. The latter are however the most significant, releasing greater amounts of these pollutants in more toxic and mobile forms. Their chemistry and dynamics in the ecosystems are presented, and the relation to the pollution problematic thereof is discussed. The concentration of heavy metals in several sites, assessed in water, soil and sediment samples, affected by different pollution sources are reviewed. These evidence how human activities impact natural media and how the pollution spreads. The pollution in each media is assessed by the concentration relative to drinking and irrigation water guidelines, and by the geoaccumulation index of soils and sediments. It is found that ore extraction and processing and metallurgical industries stand atop the most polluting sources. Given the dynamics of heavy metal cations and that, most of these are released in liquid effluents, wastewater treatment techniques for the removal of heavy metals are also surveyed and critically discussed. Economic viability at a large municipal scale and the ability to comply with strict regulations are the determining factors in the selection of these techniques. A critical discussion on the viability of such techniques is made, reviewing some literature studies and commenting on their applicability on the previously found polluted media.Copyright © 2019 Elsevier Ltd. All rights reserved.
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重金属在河湖底泥中的积聚已成为我国的一大环境问题,通过及时妥善的技术处理,可以避免重金属对环境的二次污染。基于生石灰降低底泥含水量,锯末灰初步固化,采用水泥和矿粉+水泥2种方式对生石灰-锯末灰固化后的污泥进一步固化的方法,对天津西青区某河流污染底泥开展试验。基于原子吸收分光法对试验样品进行重金属浸出浓度分析,比较水泥和矿粉+水泥固化2种方法的固化效果。研究表明,当生石灰掺入比为9%,养护2 d 时,污泥的含水率明显降低。锯末灰掺入比10% 、水泥掺入比20%、矿粉换掺水泥40%时,底泥中的 Ni<sup>2+ </sup>、 Hg<sup>2+ </sup>、 Pb<sup>2+ </sup>、 Cd<sup>2+ </sup> 4种超标重金属浸出浓度分别降低71.61%、84.85%、58.49%、77.78%,均满足相关技术规范要求。为检验固化土的种植效果,选用牛筋草和牛繁缕2种植物进行室内60 d种植试验,发现2种植物的光合作用、根部发育、生长速度都很正常。结果表明生石灰掺入比9%、锯末灰掺入比10%、水泥掺入比20%、矿粉换掺水泥40%的固化方案得到的固化土可用于绿化种植。
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The accumulation of heavy metals in the sediment of rivers and lakes has become a major environmental problem in China. On the basis of reducing the water content of sediment by adding quicklime and preliminarily solidifying by sawdust ash, the polluted sludge from a river in Tianjin was further solidified by adding cement or mineral powder plus cement as a demonstration. The leaching concentrations of heavy metals in the test samples were examined using atomic absorption spectrometry, and the curing effects of cement and mineral powder plus cement were compared. Results unveiled that treated by a dosage of 9% quicklime for two days, the contaminated sludge saw an obviously reduction in moisture content. The leaching concentrations of Ni<sup>2+</sup>, Hg<sup>2+</sup>, Pb<sup>2+</sup> and Cd<sup>2+</sup> in the contaminated sediment declined by 71.61%, 84.85%, 58.49%, and 77.78% respectively when the content of saw dust was 10%, cement was 20%, and ore powder replacing 40% of the cement, which all met the requirements of relevant technical specifications. To test the planting effect of solidified soil,<i>Eleusine indica</i> and <i>Malachium aquaticum</i> were selected for indoor planting experiment for 60 days. The photosynthesis, root development and growth rate of the two plants were normal. It can be concluded that the contaminated sediment solidified by 9% quicklime, 10% sawdust ash, 20% cement and 40% mineral powder for replacing cement can be used for greening planting.
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为修复镉污染土壤,同时资源化利用工业废渣,以水泥、赤泥、电石渣、磷石膏为原料制备了镉污染土壤固化剂。考察了龄期对固化土无侧限抗压强度、渗透系数、浸出液pH、浸出毒性的影响,并采用SEM-EDS技术观察固化土微观形貌、Tessier五步连续提取法分析重金属形态。实验结果表明,水泥、赤泥、电石渣、磷石膏的最佳掺量（以干土壤质量计）为9%,5%,1%,1%。工业废渣固化土的抗压强度和抗渗性随龄期延长而提高,浸出液pH呈先上升后平稳再下降的趋势,毒性浸出液中未检测到Cd<sup>2+</sup>。对比同等掺量的水泥固化土,工业废渣固化土的渗透系数和腐蚀性均更低。固化土中有钙矾石和水化硅酸钙生成,镉的稳定态含量较高。
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For remediation of cadmium contaminated soil and resource utilization of industrial waste residues,a solidifying agent of cadmium-contaminated soil was prepared using cement,red mud,cadmium carbide slag,and phosphogypsum as raw materials. The effects of age on unconfined compressive strength,permeability coefficient,pH value of the leachate,and leaching toxicity were investigated. The micro morphology was observed by SEM-EDS,and the heavy metal morphology was analyzed by the Tessier five-step continuous extraction method. The experimental results show that the best mixing amount （calculated by dry soil mass） of cement,red mud,calcium carbide slag and phosphogypsum in the soil are 9%,5%,1%,and 1%. The compressive strength and impermeability of the industrial waste solidified soil are increased with age,and the pH of the leachate first increased,then stabilized,and then decreased. No cadmium ions are detected in the toxic leachate. Compared with the cement solidified soil with the same mixing amount,the solidification effect of industrial waste residue is more obvious,and the permeability coefficient and corrosiveness are smaller. In addition,the generation of ettringite and calcium silicate hydrate is found in the solidified soil by SEM-EDS,and higher content of steady-state cadmium is detected by Tessier method. |
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地质聚合物是一类以SiO<sub>2</sub>和Al<sub>2</sub>O<sub>3</sub>为主要成分,经适当工艺及化学反应得到的具有非晶态三维网状结构的新型硅铝质材料。使用地质聚合物部分替代水泥用于土壤固化不仅可以减少水泥用量,还可以改善固化土的强度和耐久性。本研究采用粉煤灰基地质聚合物部分代替水泥固化粉土,分别探究不同固化剂配比、粉煤灰基地质聚合物替代水泥比例、含水量、养护时间对固化土无侧限抗压强度的影响。结果表明,粉煤灰基地质聚合物部分替代水泥对土壤的固化效果有显著提升。当固化剂含量在8%~15%(质量分数)时,固化剂含量越高,固化土的无侧限抗压强度越大,且强度增长速度越快。随着粉煤灰基地质聚合物替代水泥比例的增加,固化土的无侧限抗压强度先升高后降低。当含水率为28%、粉煤灰基地质聚合物占比为5%(质量分数)、养护时间为60 d时,固化土的无侧限抗压强度达到最大值。当粉煤灰基地质聚合物占比为10%和15%时,固化土的无侧限抗压强度随含水率的增加呈先升高后降低的趋势;当粉煤灰基地质聚合物占比为0%和5%时,固化土的无侧限抗压强度随含水率的增加而降低。随着粉煤灰基地质聚合物含量的增加,固化土应力-应变曲线斜率先增大后减小。
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Geopolymer is a new type of silica-aluminium material with amorphous three-dimensional network structure, which is obtained by appropriate process and chemical reaction with SiO<sub>2</sub> and Al<sub>2</sub>O<sub>3</sub> as main components. Using geopolymers to partially replace cement for soil solidification not only reduces the amount of cement, but also improves the strength and durability of solidified soil. In this study, fly ash-based geopolymer was used to partially replace cement to solidify powdery soil. The effects of different curing agent ratios, proportion of fly ash-based geopolymer replacing cement, water content, and curing time on the unconfined compressive strength of solidified soil were investigated. The results show that the curing effect of fly ash-based geopolymer partially replacing cement on soil is significantly improved. When the curing agent content is 8%~15% (mass fraction), the unconfined compressive strength of the solidified soil is greater, and the strength growth rate is faster. With the increase of the proportion of fly ash-based geopolymer replacing cement, the unconfined compressive strength of solidified soil increases first and then decreases. When the water content is 28%, the proportion of fly ash-based geopolymer is 5% (mass fraction), and the curing time is 60 d, the unconfined compressive strength of solidified soil reaches the maximum value. When the proportion of fly ash-based geopolymer is 10% and 15% (mass fraction), the unconfined compressive strength of solidified soil increases first and then decreases with the increase of water content. When the proportion of fly ash-based geopolymer is 0% and 5% (mass fraction), the unconfined compressive strength of solidified soil decreases with the increase of fly ash-based water content. With the increase of fly ash-based geopolymer content, the stress-strain curve slope of solidified soil first increases and then decreases.
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张庆, 董晓强, 冯亚松, 等. 新型废渣基固化剂修复污染土镍锌扩散特性研究[J]. 太原理工大学学报, 2022, 53(5): 963-970.
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李喜林, 于晓婉, 刘玲, 等. 复合制剂修复铬污染土的条件优化及微观特性[J]. 长江科学院院报, 2021, 38(7): 80-87.
针对单一还原法和固化/稳定化技术处理铬污染土效果不佳的问题,提出还原-固化/稳定化联用方法,通过单掺试验和L<sub>9</sub>(3<sup>4</sup>)正交试验,确定了还原剂、吸附剂、固化剂所组成的复合制剂的最佳配比,并采用扫描电镜对固化/稳定化铬污染土进行了微观表征。研究结果表明,复合制剂最佳配比为:CaS<sub>5</sub>用量是污染土中Cr(VI)还原为Cr(Ⅲ)所需理论还原剂量的3倍;合成沸石掺量为15%;水泥掺量为20%。扫描电镜分析结果显示,复合制剂通过还原-吸附-固化联合作用,减小了Cr(VI)和Cr(Ⅲ)对水化反应和凝硬反应的阻碍作用,强化了固化/稳定化效果,对固化体的浸出浓度降低效果显著,毒性浸出满足相关标准要求。
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