Effects of organic acids activated phosphate rock on the stabilization of lead and cadmium in soil

Abstract

Organic acids were used to activate phosphate rock (PR) via a mechanochemical wet-grinding process to prepare remediation materials for stabilizing Pb and Cd in contaminated soils. The soil samples were collected from an abandoned lead smelting site, with initial Pb and Cd concentrations of 5933.0 and 99.4 mg/kg, respectively. Material characterization revealed that organic acid activation transformed PR into porous aggregates with reduced crystallinity, while promoting the formation of amorphous phosphate minerals. Consequently, the adsorption capacity of PR for Pb and Cd was significantly enhanced. The activated PR materials were thoroughly mixed into the soil at an application rate of 5% (w/w). After a 30-day incubation, the leaching concentrations of Pb and Cd decreased from 1.120 and 0.079 mg/L to 0.011 and 0.008 mg/L, respectively. Driven by the treatment with the humic acid-activated PR (PR-HA) amendment, the immobilization efficiencies of Pb and Cd reached 82.1% and 69.9%, respectively, as indicated by the reduction in DTPA-extractable fractions. Furthermore, the amendment enhanced the soil cation exchange capacity (CEC), available phosphorus, and amorphous iron oxides, thereby facilitating the long-term stabilization of Pb and Cd. Overall, the PR-HA amendment shows great promise for the remediation of Pb and Cd-contaminated soils at smelting sites.

Keywords

heavy metals / phosphate rock / organic acid / stabilization / soil remediation

References

[1] He M-s, Zhang Z, Wang M, et al. . A review of hydroxyapatite synthesis for heavy metal adsorption assisted by machine learning [J]. Journal of Hazardous Materials, 2025, 481: 136525

[2] Gao W-y, Wu K-k, Chen T, et al. . Heavy metal (loid)s transformation in dust at a lead smelting site [J]. Journal of Central South University, 2024, 31(4): 1036-1049

[3] He J, Li C-x, Tan X-y, et al. . Driving factors for distribution and transformation of heavy metals speciation in a zinc smelting site [J]. Journal of Hazardous Materials, 2024, 471: 134413

[4] Gao W-y, Xiang C, Wu C, et al. . Unveiling heavy metal(loid) contamination and migration at an abandoned smelting site: Integrated geophysical and hydrological analyse [J]. Chemical Engineering Journal, 2024, 500: 156853

[5] Luo X-h, Wu C, Lin Y-c, et al. . Soil heavy metal pollution from Pb/Zn smelting regions in China and the remediation potential of biomineralization [J]. Journal of Environmental Sciences, 2023, 125: 662-677

[6] Min T, Lu T, Zheng S, et al. . Efficiency of metal oxides in reducing heavy metal uptake in typical crops: A machine learning-assisted meta-analysis [J]. Journal of Cleaner Production, 2025, 491: 144856

[7] Da Silva Rodrigues Viana R, Chagas J K M, Paz-Ferreiro J, et al. . Enhanced remediation of heavy metal-contaminated soils using biochar and zeolite combinations with additives: A meta-analysis [J]. Environmental Pollution, 2025, 367: 125617

[8] Ahmed W, Mehmood S, Mahmood M, et al. . Simultaneous immobilization of lead and arsenic and improved phosphorus availability in contaminated soil using biochar composite modified with hydroxyapatite and oxidation: Findings from a pot experiment [J]. Environmental Research, 2023, 235: 116640

[9] Sha H-c, Li J, Wang L-q, et al. . Preparation of phosphorus-modified biochar for the immobilization of heavy metals in typical lead-zinc contaminated mining soil: Performance, mechanism and microbial community [J]. Environmental Research, 2023, 218: 114769

[10] Zhang M, Wang X-m, Wei C-y, et al. . Effects of exogenous phosphates on speciation and bioavailability of arsenic and cadmium in farmland soils [J]. Journal of Soils and Sediments, 2023, 23(4): 1832-1843

[11] Hong C O, Lee D K, Kim P J. Feasibility of phosphate fertilizer to immobilize cadmium in a field [J]. Chemosphere, 2008, 70(11): 2009-2015

[12] Zeng G-m, Wan J, Huang D-l, et al. . Precipitation, adsorption and rhizosphere effect: The mechanisms for Phosphate-induced Pb immobilization in soils: A review [J]. Journal of Hazardous Materials, 2017, 339: 354-367

[13] Song Z-w, Zhang Z, Luo C-y, et al. . High-efficiency stabilization of lead in contaminated soil by thermal-organic acid – activated phosphate rock [J]. Environmental Science and Pollution Research, 2022, 29(32): 49116-49125

[14] Mignardi S, Corami A, Ferrini V. Evaluation of the effectiveness of phosphate treatment for the remediation of mine waste soils contaminated with Cd, Cu, Pb, and Zn [J]. Chemosphere, 2012, 86(4): 354-360

[15] Antelo J, Arce F, Fiol S. Arsenate and phosphate adsorption on ferrihydrite nanoparticles. Synergetic interaction with calcium ions [J]. Chemical Geology, 2015, 410: 53-62

[16] Li C-x, Yuan S-x, Li H-f, et al. . Effect of slow-release phosphate on stabilization and long-term stability of Zn and Cd in soil [J]. Transactions of Nonferrous Metals Society of China, 2025, 35(6): 2091-2104

[17] Mao X-y, Lu Q, Mo W, et al. . Phosphorus availability and release pattern from activated dolomite phosphate rock in central Florida [J]. Journal of Agricultural and Food Chemistry, 2017, 65(23): 4589-4596

[18] Zhu J, Li M, Whelan M. Phosphorus activators contribute to legacy phosphorus availability in agricultural soils: A review [J]. Science of the Total Environment, 2018, 612: 522-537

[19] Yang F, Zhang S-s, Song J-p, et al. . Synthetic humic acids solubilize otherwise insoluble phosphates to improve soil fertility [J]. Angewandte Chemie, 2019, 131(52): 18989-18992

[20] De Oliveira Mendes G, Murta H M, Valadares R V, et al. . Oxalic acid is more efficient than sulfuric acid for rock phosphate solubilization [J]. Minerals Engineering, 2020, 155: 106458

[21] Li X, Feng J-p, Zhu X-l, et al. . Organic acid release and microbial community assembly driven by phosphate-solubilizing bacteria enhance Pb, Cd, and as immobilization in soils remediated with iron-doped hydroxyapatite [J]. Journal of Hazardous Materials, 2025, 488: 137340

[22] Tian D, Zhang X-r, Wang L-y, et al. . Lead remediation is promoted by phosphate-solubilizing fungi and apatite via the enhanced production of organic acid [J]. Frontiers in Bioengineering and Biotechnology, 2023, 11: 1180431

[23] Wei W, Cui J, Wei Z-gui. Effects of low molecular weight organic acids on the immobilization of aqueous Pb(II) using phosphate rock and different crystallized hydroxyapatite [J]. Chemosphere, 2014, 105: 14-23

[24] Jiang G-j, Liu Y-h, Huang L, et al. . Mechanism of lead immobilization by oxalic acid-activated phosphate rocks [J]. Journal of Environmental Sciences, 2012, 24(5): 919-925

[25] Zhang Z, Guo G-l, Wang M, et al. . Enhanced stabilization of Pb, Zn, and Cd in contaminated soils using oxalic acid-activated phosphate rocks [J]. Environmental Science and Pollution Research, 2018, 25(3): 2861-2868

[26] Debela F, Arocena J M, Thring R W, et al. . Organic acids inhibit the formation of pyromorphite and Zn-phosphate in phosphorous amended Pb- and Zn-contaminated soil [J]. Journal of Environmental Management, 2013, 116: 156-162

[27] Yang J Y, Yang X E, He Z L, et al. . Effects of pH, organic acids, and inorganic ions on lead desorption from soils [J]. Environmental Pollution, 2006, 143(1): 9-15

[28] Wang M, Zhang Z, Ren J, et al. . Microscopic evidence for humic acid induced changes in lead immobilization by phosphate in a counterdiffusion system [J]. Journal of Hazardous Materials, 2017, 330: 46-51

[29] Yao W-b, Huang L, Yang Z-h, et al. . Effects of organic acids on heavy metal release or immobilization in contaminated soil [J]. Transactions of Nonferrous Metals Society of China, 2022, 32(4): 1277-1289

[30] Xu D-m, Fu R-b, Liu H-q, et al. . Current knowledge from heavy metal pollution in Chinese smelter contaminated soils, health risk implications and associated remediation progress in recent decades: A critical review [J]. Journal of Cleaner Production, 2021, 286: 124989

[31] Wang Y-k, Zhang Z, Li Y-y, et al. . Available heavy metals concentrations in agricultural soils: Relationship with soil properties and total heavy metals concentrations in different industries [J]. Journal of Hazardous Materials, 2024, 471: 134410

[32] Fu H-j, Li X-x, Dai G-q, et al. . Performance of oxalate-doped hydroxyapatite as well as relative contribution of oxalate and phosphate for aqueous lead removal [J]. Science of the Total Environment, 2023, 857: 159596

[33] Huang L, Mao X Y, Wang J, et al. . The effect and mechanism of improved efficiency of physicochemical prorelease treatment for low grade phosphate rock[J]. Journal of Soil Science and Plant Nutrition, 2014, 14: 316-331

[34] Li L, Wang W-h, Jiang Z-w, et al. . Phosphate in aqueous solution adsorbs on limestone surfaces and promotes dissolution [J]. Water, 2023, 15(18): 3230

[35] Ke W-s, Zeng J-q, Zhu F, et al. . Geochemical partitioning and spatial distribution of heavy metals in soils contaminated by lead smelting [J]. Environmental Pollution, 2022, 307: 119486

[36] Huang G-y, Gao R-l, You J-w, et al. . Oxalic acid activated phosphate rock and bone meal to immobilize Cu and Pb in mine soils [J]. Ecotoxicology and Environmental Safety, 2019, 174: 401-407

[37] Jiang Z, Nie K, Arinzechi C, et al. . Cooperative effect of slow-release ferrous and phosphate for simultaneous stabilization of As, Cd and Pb in soil [J]. Journal of Hazardous Materials, 2023, 452: 131232

[38] Klučáková M, Pavlíková M. Lignitic humic acids as environmentally-friendly adsorbent for heavy metals [J]. Journal of Chemistry, 2017, 2017: 7169019

[39] Qian G-r, Xu L, Li N, et al. . Enhanced arsenic migration in tailings soil with the addition of humic acid, fulvic acid and thiol-modified humic acid [J]. Chemosphere, 2022, 286: 131784

[40] Xu J-c, Huang L-m, Chen C-y, et al. . Effective lead immobilization by phosphate rock solubilization mediated by phosphate rock amendment and phosphate solubilizing bacteria [J]. Chemosphere, 2019, 237: 124540

[41] Seshadri B, Bolan N S, Choppala G, et al. . Potential value of phosphate compounds in enhancing immobilization and reducing bioavailability of mixed heavy metal contaminants in shooting range soil [J]. Chemosphere, 2017, 184: 197-206

[42] Liu B-b, He Z-l, Liu R-l, et al. . Comparative effectiveness of activated dolomite phosphate rock and biochar for immobilizing cadmium and lead in soils [J]. Chemosphere, 2021, 266: 129202

[43] Chen X-m, Ren Y-q, Li C, et al. . Study on factors influencing the migration of heavy metals from soil to vegetables in a heavy industry city [J]. Sustainability, 2024, 16(24): 11084

[44] Xu D-c, Shen Z-j, Dou C-m, et al. . Effects of soil properties on heavy metal bioavailability and accumulation in crop grains under different farmland use patterns [J]. Scientific Reports, 2022, 12: 9211

[45] Zeng Y, Farooq T H, Yuan C-l, et al. . Organic-based remediation of heavy metal-contaminated soils in the Taojia river basin affected by long-term non-ferrous mining and logging activities [J]. Frontiers in Plant Science, 2025, 16: 1486575

[46] Ma C, Liu X-mei. Immobilization of Pb and Cd in red soil using Fe – Mn modified sugarcane bagasse biochar: Mechanisms and plant uptake [J]. Environmental Geochemistry and Health, 2026, 48(6): 250

[47] Marzi M, Towfighi H, Shahbazi K, et al. . Study of arsenic adsorption in calcareous soils: Competitive effect of phosphate, citrate, oxalate, humic acid and fulvic acid [J]. Journal of Environmental Management, 2022, 318: 115532

[48] Colombo C, Palumbo G, He J-z, et al. . Review on iron availability in soil: Interaction of Fe minerals, plants, and microbes [J]. Journal of Soils and Sediments, 2014, 14(3): 538-548

RIGHTS & PERMISSIONS

Central South University