*2.5. Solidification Experiment*

After the flocculation-settling experiment, the sediment with the lowest water content after settling was subjected to the solidification experiment. The supernatant of the experimental group was poured out, and a solidification agent was added to the sediment for stirring, wherein the stirring speed was 450 rpm, and the stirring was performed for 2 min. Subsequently, the sediment was layered into the mold. The inner diameter and height of the mold are 39.1 mm and 80.0 mm, respectively.

According to results with PAM pretreatment in Section 3, the sediment pretreated with APAM 7126 (0.25%) had the lowest water content. For the composite pretreatment experiments, the combined addition of FeCl3·6H2O (3%) and APAM 7126 (0.10%) obtained the sediment with lower water content. Therefore, the sediment obtained from these two sets of experiments was used for solidification experiments. The solidification scheme is shown in Table 4.

**Table 4.** Solidification scheme of sediment.


<sup>1</sup> The dosage is calculated as the ratio of the dry mass of solidification agent to the dry mass of slurry.

The moist room YH-60B type (produced by Beijing central North Road Instrument Equipment Co., Ltd., Beijing, China) was used in the solidification experiment. The curing conditions were a temperature of 20 ◦C and humidity of >95%. After a set curing time, an unconfined compressive strength experiment was performed.
