## 4 Discussion  
The pH (Figure 3a) increased due to the alkaline nature and liming effects of OPC, FAC, and ZEC. The influence of such amendments is more evident in mining activities, as mentioned by [PERSON] [22]. Generally, OPC, FAC, and ZEC contain significant amounts of alkaline metals (Ca\({}^{2+}\) and Mg\({}^{2+}\)). These alkaline metal ions are then converted and dissolved into metal oxides, metal hydroxides, and carbonates during the hydrolysis process, thereby increasing the soil pH [63]. These results agree with several previous reports [22, 64, 65]. A similar trend was observed in the soil CEC (Figure 3b), which increased with an increase in the OPC, FAC, and ZEC application rates. Soil CEC reflects the sum of negative charges on the material surface which can be balanced by exchangeable cations [62]. Higher soil CEC values indicate the development of a more negative charge in the treated soils. OPC, FAC, and ZEC contain appreciable amounts of inorganic constituents (Ca\({}^{2+}\), Mg\({}^{2+}\), and Si) released into the soil solution, promoting soil CEC increase and providing available nutrients for plant growth [66]. However, OPC, FAC, and ZEC applications did not increase the SOM (Figure 3c) compared to control, which may be attributed to the fact that the main component of waste cement is inorganic calcium carbonate. Nevertheless, applying OPC, FAC, and ZEC can additionally loosen the soil structure, enhance soil aeration, provide space for soil microorganism activities, and accelerate the decomposition and mineralization of organic matter [67]. The increased values of pH and CEC suggest that a boost in the immobilization of heavy metals could be expected. Figure 8: Effect of amendments on the plant antioxidant enzymatic activities: (**a**) peroxidase (POD) activities, (**b**) catalase (CAT) activities, (**c**) superoxide dismutase (SOD) activities and (**d**) malondialdehydehyde (MDA). Treatments: control (CK), cement paste (OPC), fly ash cement paste (FAC) and zeolite cement paste (ZEC). OPC, FAC, and ZEC could all effectively reduce the concentration of Cd extracted by DTPA (Figure 4), and the degree of reduction had a direct relationship with the amount added. The occurrence of this phenomenon was mainly due to the fact that the waste cement materials are alkaline and can hydrolyze hydroxyl ions, Ca\({}^{2+}\) and CO\({}_{3}\)\({}^{2+}\) to precipitate Cd ions in the soils. At the same time, the three kinds of waste cement also have a relatively high content of Si, which can also effectively fix Cd ions in the soils. The three waste cements increased the pH of soils and shifted the soil particle charge towards being more negative, thus increasing the fixation or sorption of Cd on soil particles. FDA is diffused through cell membranes and then hydrolyzed by proteases, lipase and esterases to release fluorescent proteins [68]. FDA hydrolysis can reflect the transformation of organic matter in the soil and be used to measure the soil's total microbial activity. Therefore, FDA hydrolysis is also an important indicator for monitoring soil health. Increased FDA hydrolysis (Figure 5a) could have resulted from the decreased Cd availability, mainly due to its remediation by the addition of waste cement on Cd-contaminated soil. It benefited the growth of soil microorganisms, improving microbial activity, which directly or indirectly improved the FDA hydrolysis. Soil catalase activity indicates soil oxidation\(-\)reduction capacity [69] and is related to soil microenvironment and soil organic matter. Compared to control, the catalase activity (Figure 5b) did not exhibit a substantial increase. The limited change in catalase activity was consistent with the non\(-\)significant changes observed in soil organic matter. The catalase activity was partly due to the effect of waste cement on soil organic matter, which had no beneficial effects on soil biology. In the present study, waste cement did not affect soil catalase activity and soil organic matter.