**6. Mitigation methods**

Some of the important techniques to mitigate radon gas in underground mines are discussed below.

### **6.1 Sealant coating**

The major sources of radon gas in non-uranium underground mines (with uranium mineralization) are the drift walls, floor, and roof. Shotcreting or applying radon sealants to the walls and roof effectively minimizes radon gas emissions into the mine atmosphere. The effectiveness of sealant coating in controlling the radon gas depends on the size of the capillary in which the acrylics (contained in the sealants) form barriers to prevent the escape of radon gas [12].

## **6.2 Bulkhead**

Isolation of mined-out areas using bulkheads is one of the popular methods of controlling radon gas emissions into the active mine workings. Bulkheads prevent the contaminated air of mined-out regions containing high radon gas concentrations from mixing with the fresh air. Loring and others [13] reported that styrofoam and shotcrete/concrete bulkheads are used in a panel cave mine for a temporary and permanent sealing purpose, respectively. These bulkheads are installed at a 60-degree layback angle of the planned cave area to minimize damage to the bulkheads during the caving process. As the bulkheads are not leak proof, bleeder pipes creating a negative pressure inside the bulkhead area and connected to the main exhaust ventilation system can also be an effective measure [13]. **Figure 7** shows the typical designs of bulkheads.

### **6.3 Mine pressurization by mechanical ventilation**

Mine pressurization can also play an important role in controlling radon gas emissions in underground workings, especially near-working faces. In a forced ventilation system, which is considered quite effective for control of radon gas in the mine environment, fresh air is pumped into underground workings with the help of fans; this follows the path of least resistance taking the contaminants along with it and out of the mine. In the forced ventilation system, the direction of seepage is toward the rock surface, causing less radon to be released.

Studies [13] have shown that a successful blend of positive and negative pressure systems in a panel cave mine effectively reduces the radon gas concentrations at the production level. Negative pressure on the cave top minimizes the escape of radon gas from the broken ore to the production levels. Positive pressurization in the undercut levels also reduces the escape of radon gas into the working

**Figure 7.** *Typical designs of bulkheads [14].*

areas. Mine pressurization greatly depends on the porosity and permeability of the broken rock/ore for its effectiveness in controlling radon concentrations in the underground environment. **Figure 8** shows a typical cave ventilation system in a block/panel cave mine.

Computational fluid dynamic (CFD) simulation studies by Kayode et al. [15] showed the effect of an undercut ventilation system on radon gas distribution in the production drift and cave. It was observed that the air flowing through the cave transports some of the radon generated within the cave into the production drift, increasing the production drift concentration. However, in the absence of undercut ventilation, radon concentration decreases significantly within the production drift

**Figure 8.**

*A typical cave ventilation system in a panel/block cave mine.*

### *Radon in Underground Mines DOI: http://dx.doi.org/10.5772/intechopen.101247*

but increases inside the cave. The radon growth through the production drifts is nonlinear due to differences in the source of radon. Maintaining a negative pressure on top of the cave and undercut pressurization significantly reduces radon concentration in the production drift. However, maintaining a negative pressure on top of the cave is not very effective without undercut pressurization. An increase in air volume flow rate reduces radon concentration through the production drifts; based on the drift configuration for radon source, different empirical relationships relate airflow and working level for each drift.

The knowledge of airflow behavior and system characteristics is vital in ventilating the block cave operations and reducing radon concentrations. Using field observations and laboratory experiments (scale model studies), Pan [16] investigated the effects of porosity, material size combinations, additional fan, ventilation devices, and undercut structure on cave airflow resistance. The study found that the cave airflow resistance increases with a decrease in porosity and particle size, additional fan operation, regulator installation, and air gap reduction in the undercut drifts. An additional fan operation can contribute extra total airflow through the system, but regulators will not increase the total airflow in the system; the air gap observed in the undercut drifts might lead to less airflow through the production drifts.

Rahul et al. [17] investigated the effect of changes in the bulk porosity of the broken rock on the cave airflow resistance using the computational fluid dynamics (CFD) approach. This study reveals that porosity plays a vital role in changing the resistance offered by the broken rock to the airflow leaking into the cave. The airflow resistance increases as the porosity of the broken rock pile decreases. The resistance of the block cave mine changes dynamically with the bulk porosity of the broken rock.

Jha et al. [18] studied the utility of different fans in reducing the radon concentration within the drifts using a physical scale model and CFD simulations. It was observed that the combination of main and cave fan is optimal in minimizing the gas concentration within the drifts. Observations of the scaled model also show that a fully operational cave fan significantly reduced the gas concentrations within the drifts. The study suggests using main fan in conjunction with a cave fan to minimize the gas concentration within the drift.

Erogul et al. [19] investigated the impact of air gap geometries on cave resistance and radon emissions using the CFD approach. This study reported an interesting airflow behavior within the air gap zone; initially, the airflow resistance increases up to a certain height and drops as the air gap height increases further.

### **6.4 Radon adsorption on activated carbon**

Radon gas can be adsorbed by activated carbon, commonly known as a charcoal bed. The capacity of a charcoal bed to adsorb radon depends on the temperature and moisture content of the incoming air. Karunakara et al. [20] demonstrated that a coconut shell-based activated charcoal system can be used for designing effective and reliable radon mitigation systems. Degassing properties of the charcoal indicate its reusability potential. Adsorption of radon by activated carbon can also significantly reduce ventilation air requirements. **Figure 9** shows the experimental setup for studying radon adsorption in a charcoal bed.

### **6.5 Ground freezing**

Mine water is another source of radiation in underground mines. Artificial ground freezing is an excavation support method that involves the use of refrigeration to convert *in situ* pore water into ice [21]. Yun and others [22] reported that artificial ground freezing, to form a frozen curtain between the water-bearing

**Figure 9.** *Experimental setup for studying radon adsorption in charcoal bed [20].*

sandstone and the ore body at McArthur River mining operation in Canada, helped prevent high-pressure, radon-bearing water from entering into the mine workings. **Figure 10** shows a schematic of a typical ground freezing technique.
