Effect of Microbial-Modified Phosphogypsum on Properties of Supersulfated Cement

doi:10.16552/j.cnki.issn1001-1625.2025.1025

Abstract

Abstract:

In the context of global carbon peaking and carbon neutrality goals， the development of low-carbon， low-energy-consumption cementitious materials has become an important trend in the field of building materials. Supersulfated cement （SSC）， as a green cementitious material mainly composed of granulated blast-furnace slag， phosphogypsum and a small amount of cement clinker， has the advantages of low calcination energy consumption and high industrial solid waste utilization. However， untreated phosphogypsum contains harmful impurities such as phosphorus and fluorine， which seriously inhibit the hydration process of SSC， leading to long setting time and low early strength， limiting its large-scale engineering application. Traditional modification methods such as water washing and alkali washing have problems such as low impurity removal efficiency， high energy consumption， and secondary pollution.This study aims to systematically explore the effects of water washing， alkali washing， microbial treatment and microbial-alkali synergistic treatment on the macro-performance and microstructure of SSC， and reveal the enhancement mechanism of microbial modification. On the basis of the optimized mix ratio of m（slag）∶m（phosphogypsum）∶m（cement clinker）=0.84∶0.13∶0.03， the standard consistency water demand， setting time， and compressive strength of SSC were tested in accordance with Chinese national standards. The hydration products， micromorphology， pore structure and thermal stability were characterized by XRD， SEM， MIP and TG/DTG.The results show that all modification treatments can effectively improve the performance of SSC， and the microbial-alkali synergistic treatment shows the best effect. Microbial treatment increases the standard consistency water demand of SSC， shortens the initial and final setting time， which are about 20% and 30% shorter than those of the untreated group， and significantly improves the compressive strength. Compared with the control group， the 3 d compressive strength increases by 298%~349%， and the 28 d compressive strength still increases by 40%~58%. Microbial modification removes 40.24%~53.33% of total phosphorus and 34.91%~48.11% of fluoride impurities， reduces the median particle size of phosphogypsum， raises the pH value of the pore solution by about 0.98 units， and promote the formation of C-S-H gel， ettringite and calcium carbonate. Microscopic characterization shows that microbial treatment optimizes the pore structure， increases the proportion of harmless pores below 20 nm， reduces the total porosity， and makes the matrix denser.The innovation of this study lies in the first systematic comparison of multiple modification methods of phosphogypsum， clarification of the evolution pattern of bacteria in the hydration process of SSC. Bacterial cell walls act as nucleation sites to adsorb Ca²?， and the lysed organics further promote biomineralization， forming a synergistic mechanism of impurity removal， alkalinity improvement， nucleation promotion and pore filling. This research provides a green and efficient modification route for the high-value utilization of phosphogypsum， enriches the application theory of biomineralization in cement-based materials， and offers important academic value and engineering guidance for the development of high-performance low-carbon cement.

Key words: microorganism, phosphogypsum, supersulfated cement （SSC）, mechanical property, microstructure

CLC Number:

TU528

REN Jun, YAN Yunxiao, LI Miaoyuan, TIAN Zhenhe, ZHAO Lixing, WANG Dafu. Effect of Microbial-Modified Phosphogypsum on Properties of Supersulfated Cement[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(5): 1671-1681.

Figures/Tables 18

Fig.1 XRD patterns of raw materials

Table 1 Chemical composition of raw materials

Material	Mass fraction/%
Material	Na₂O	MgO	Al₂O₃	SiO₂	P₂O₅	CaO	TiO₂	Fe₂O₃	SO₃	K₂O	F
RPG	0.11	0.11	0.36	9.86	1.18	31.13	0.06	0.06	53.05	—	0.83
Slag	0.64	7.79	14.68	33.17	—	35.52	—	0.48	2.71	0.58	—
Cement clinker	0.40	3.21	5.21	21.06	—	63.46	—	3.82	0.58	0.65	—

Fig.2 Microbial treatment process of phosphogypsum

Table 2 Microbial treatment scheme

Code	RPG content/g	H₂O content/mL	0.5% NaOH content/mL	Washing liquid content/mL	Bacterial concentration content/（CFU·mL^-1）
RPG	1
WPG	1	3
ARPG	1		3
RPG-B1	1		3	3	3.3×10⁶
WPG-B1	1		3	3	3.3×10⁶
ARPG-B1	1		3	3	3.3×10⁶

Table 3 Mix ratio of SSC

Code	Slag	Phosphogypsum	Cement clinker	Mixing liquid
RPGC	0.84	0.13 RPG	0.03	0.33
WPGC	0.84	0.13 WPG	0.03	0.33
ARPGC	0.84	0.13 ARPG	0.03	0.33
RPGC-B1	0.84	0.13 RPG-B1	0.03	0.33
WPGC-B1	0.84	0.13 WPG-B1	0.03	0.33
ARPGC-B1	0.84	0.13 ARPG-B1	0.03	0.33

Fig.3 Particle size distribution of phosphogypsum before and after treatment

Fig.4 Removal ratio of total phosphorus and fluorine impurities of phosphogypsum before and after treatment

Fig.5 Standard consistency water requirement of SSC

Fig.6 Initial setting and final setting time of SSC

Fig.7 pH value of SSC pore solution at different ages

Fig.8 Compressive strength of SSC at 3， 7， and 28 d

Fig.9 XRD patterns of SSC

Fig.10 SEM images of SSC at 7 d

Fig.11 SEM images of SSC at 28 d

Fig.12 Cumulative porosity curves of SSC at 28 d

Fig.13 Pore size distribution of SSC at 28 d

Fig.14 TG/DTG curves of SSC at 28 d

Fig.15 Schematic diagram of mechanism of strength enhancement：（a） bacterial mineralization produces MICP gel；（b） cell wall provides nucleation sites；（c） bacterial lysis provides nucleation sites

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