## 3 Results and Discussion
### Performance Characterization of Dust Suppressant  
#### 3.2.1 Moisture Absorption and Retention Performance Test  
In order to verify the moisture retention and hygroscopicity of the dust suppressor under natural conditions, the moisture absorption and retention performance tests for dust suppressant were conducted for five consecutive days. Variation curves of temperature and moisture during the test are shown in Figure 7a,b. The water loss rate and the moisture content rate of samples were calculated, respectively, and their variation curves are shown in Figure 7c,d.  
According to Figure 7a,c, under natural conditions, the water loss rate for the sample sprayed with dust suppressant was significantly lower than that of the sample with pure water. The water loss rate of the sample sprayed with pure water was up to 100% on the second day, showing that its water retention effect was very poor. The water loss rate and the water loss speed of samples sprayed with dust suppressant were obviously lower than samples with pure water in the first two days. Due to the constantly changing moisture during the test, the water loss rate of samples with dust suppressant fluctuated between  
Figure 7: (**a**) Changes in ambient temperature and moisture during moisture retention test; (**b**) changes in ambient temperature and moisture during hygroscopicity test; (**c**) variation curves of water loss rate for samples under natural conditions; (**d**) variation curves of moisture content rate for samples under natural conditions.  
86% and 89% during the third to fifth days. During the experiment, the air's relative humidity in daytime ranged from 22.5% to 42.5% and the temperature ranged from 20.5 \({}^{\circ}\)C to 23 \({}^{\circ}\)C. The air humidity was the lowest on the fourth day and the water loss rate reached its maximum value on that day. However, the water loss rate of samples sprayed with dust suppressant was obviously lower than samples sprayed with pure water. Therefore, the dust suppressant demonstrated a better moisture retention effect.  
According to Figure 7b,d, under natural conditions, the moisture content rate of samples sprayed with dust suppressant was obviously higher than samples sprayed with pure water. The maximum moisture content rate of samples sprayed with pure water was only 0.25% over 3 days, and their increment in moisture content was 0.25%--approximately 0%, which shows a very poor hygroscopicity. The moisture content rate of samples sprayed with dust suppressant fluctuated between 8.26% and 9.33% over 3 days, and their increment in moisture content was 1.07%, both of which were obviously higher than samples sprayed with pure water. The temperature and the humidity exhibited constant variation during the test, with the humidity ranging from 27% to 43% and the temperature ranging from 25 \({}^{\circ}\)C to 28 \({}^{\circ}\)C. As a result, the moisture content rate of samples sprayed with dust suppressant fluctuated around 8%. The air humidity was lower at the 48 th hour and the moisture content rate of samples decreased slightly. However, with the increase of humidity, the moisture content rate of those samples also increased. Generally, the moisture content rate and the increment of samples sprayed with dust suppressant were obviously higher than samples sprayed with pure water. Therefore, the dust suppressant demonstrated good hygroscopicity.