UNIVERSITY OF CAPETOWN
FACULTY OF ENGINEERING AND BUILT ENVIRONMENT
DEPARTMENT OF CHEMICAL ENGINEERING
MSC RESEARCH PROJECT
TOPIC: EXPOSURE MONITORING OF MINE DUST AND
TOXIC SUBSTANCES
TITLE: INVESTIGATING WATER ADDITIVES THAT CAN
BE USED TO IMPROVE CAPTURING OF RESPIRABLE
DUST AND CRYSTALLINE SILICA IN UNDERGROUND
MINES DURING DUST SUPPRESION
STUDENT: LOVEJOY NYONI
SUPERVISOR: DR C MANGUNDA
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TITLE: EXAMINING WATER ADDITIVES THAT CAN BE USED TO
IMPROVE CAPTURING OF RESPIRABLE DUST AND CRYSTALLINE
SILICA IN UNDRGROUND MINES DURING DUST SUPPRESION
1.1 AIM
To examine the use of silica suppressants in enhancing water’s ability to control respirable
silica dust.
1.2 SPECIFIC OBJECTIVES
1. To review the characteristics of crystalline silica dust in water
2. To study the properties of different additives that can be used to enhance water-dust
contact and select the most effective additive for laboratory testing.
3. To examine the water spray systems for dust control
1.3 BACKGROUND
Mining industry is the economic backbone for many countries around the world.
(Elizaberth,2011) However, the major drawback posed by the operations presents serious
health and environmental problems. Mining operations generate enormous amounts of dust
which are environmentally unfriendly resulting in heavy air pollution. (Ghose, 2001) The
largest quantities of airborne dust are usually produced in mining facilities by several
mechanical operations including blasting, drilling, scrapping, comminution and transportation.
(Prostański, 2015). Dust move together with the ventilation air (Bhaskar, 1986) and it settles
at the wall and equipment such as excavators (Nawrat et al.2002). The dust from mining
operations does not only affect the mining vicinity, but the environment and communities
around the mining area.
In the process of mining mineral raw materials, workers are exposed to elevated levels of
noxious aerosols including respirable dust and crystalline silica. (M Biffi, 2000). Exposure to
the dust presented in the ventilation air poses a threat to health eventually leading to debilitating
respiratory diseases that can affect the health of workers and it has undesirable influence on
working conditions. Numerous research studies have been conducted to combat the health
problems presented by mining operations such as rock blasting and polishing, but they continue
to escalate. It is important that the mining companies embrace technology in trying to meet
health requirements and governmental regulation prescriptions. Major sources of dust are open
pit mines, stockpiles, mine dumps, ore processing and metal extraction plants. (Sandton, 2006)
This presents a gap in developing technology and framework to curb the global challenges
faced by mine workers and mining communities.
The actuality of all efforts aiming at combatting of toxic dust particles to health, linked with
the silicosis and pneumoconiosis morbidity, requires personal monitoring of the dust exposure
(Lebecki and Bywalec, 1998). The outcome of the monitoring gives the basis for undertaking
effective preventive measures depending on the type of work performed. The mining laws in
South Africa are predominantly regulated by the Mineral and Petroleum Resources
Development Act 28 of 2002 (MPRDA). There are several other pieces of legislation which
deal with issues such as royalties (the Mineral and Petroleum Resources Royalty Act, 2008),
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title registration (the Mining Titles Registration Act, 1967), and health and safety (the Mine
Health and Safety Act, 1996). These regulations specify the maximum and minimum
concentrations of dust and respirable crystalline silica. In terms of the occupational exposure
limits contained in the guidelines for the generation of Mandatory Codes of Practice in terms
of Section 9(2) of the Mine Health and Safety Act, 1996 (Act No. 29 of 1996), exposure to
silica dust is limited as follows: Crystalline Silica: 0,1 mg/m³(8h), amorphous silica (Inhalable)
6,0 mg/m³(8h) and amorphous Silica (Respirable) 3,0 mg/m³(8h) (Biffi, 2008)
There are various means which can be used to determine the amount of respirable dust and
crystalline silica inhaled by workers such as mineralogical test methods, including X-Ray
Diffraction (XRD). According to NIOSH, CDC, Safety and Health, in order to quantify a
miner’s exposure to noxious substances, monitoring is one of the effective methods. Personal
monitoring is a widely used approach to evaluate worker exposure, where a sample or multiple
samples taken from the breathing area of the worker and at that of time that can be increased
to a full shift during that sampling period. A gravimetric-based dust monitor is often used to
determine the levels of silica with use of filters and sampling instruments. The whole area can
be monitored with multiple samplers used to characterize the level of toxic substances in the
air during mining operations. Lastly, monitoring a specific mining activity considered to be as
a source of respirable dust enables for a total understanding of the task and the required control
technologies. The result of the monitoring gives the basis for undertaking effective preventive
measures depending on the type of works performed (Lebecki and Bywalec, 1998).
Continuous improvement of dust suppression methods is necessary to achieve the diminishing
of silicosis and pneumoconiosis probability in underground mines.
1.4 PROBLEM STATEMENT
Despite mining industry playing a major role in the economic stability of many developing
countries, the resulting negative impacts of mining operations continue to threaten the health
of many citizens. Silica or quartz is the most abundant mineral on the earth and is found in
almost all minerals mined. Crystalline silica is a cause of concern amongst other toxic dusts.
Coal is a versatile mineral that is often mined, and it comprises of organic and mineral matter.
Respirable coal mine dust normally contains a small proportion (usually < 5%) of quartz or
silicates, mostly from dirt bands within the coal stratum (Stanton et al, 2006). It was reported
that the average measured silica content of South African coal seams was 3.5% (Biffi, 2003).
Silicosis is a debilitating and often fatal coal worker's occupational lung disease caused by the
prolonged exposure and inhalation of free crystalline silica dust (quartz, tridyrnite, and
cristobalite) (Varon et al, 2008). The respirable dust particles and crystalline silica are tiny, less
than 10 microns in diameter (for comparison a human hair is 40 – 50 microns in
diameter). (Stanton et al, 2006). It has been found that patients with a history of silicosis are at
a high risk of developing tuberculosis. Minimising the cases of silicosis will result in a
subsequent decrease in the cases for tuberculosis.
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1.5 JUSTIFICATION
Social and economic impacts of silicosis attract attention of social leaders, economists, health
policy makers and labour organisations. The economy of a state is greatly impacted by the
disability and death of productive population. Absenteeism, loss of qualified labour, reduced
productivity and burden on workers’ compensation system negatively affects the state
economy. Silico-tuberculosis among working and former working miners (Knight et al, 2020)
continue to become a health problem. There is an increased incidence of tuberculosis with the
increasing severity of silicosis (Palash, 2016) and there has been no decline in silicosis
prevalence. Silicosis is an irreversible condition and has no cure, although there are treatment
options available to ease the symptoms and related complications. To achieve this objective,
research is conducted to identify and develop improved dust control technologies, which can
then be implemented by industry to reduce mine workers' respirable dust exposure.
1.6 METHODOLOGY
Approved continuous personal devices (CPDM) will be used to obtain required dust
measurements. A gravimetric analysis instrument is a continuous personal sampling tool that
is worn by a worker and gives a display of a cumulative-mass concentration of quartz in the
mine atmosphere. (Walker et al, 2021). Samples are collected onto filters that are taken to a
laboratory for quartz analysis using the available spectroscopy.
Bulk samples of settled fine dust in the vicinity of each respirable dust sampler are a rough
representation of the aggregate dust present in the atmosphere. These bulk samples will be
stored in sealed containers for subsequent laboratory processing and analysis (Cauda et al,
2018)
Water is used to suppress dust produced by underground mining operations and it is typically
applied to the blade through one or two nozzles to suppress dust emissions. The source of
water may be a portable pressurized tank or a hose. The recommended flow rate is 0.5 liters of
water per minute to suppress dust. Dust is hydrophobic, meaning it fails to mix easily with
water. Wet method can not provide a total containment silica dust. To combat this, a silica dust
suppressant is required, to break down the barrier between the dust and water. The suppressant
commonly used in USA mining companies is the product NeSilex which contains specially
formulated surfactants, wetting and agglomerating agents causing dust particulates to saturate
and attract to each other. Examples of dust depressants are magnesium chloride and calcium
chloride. Both groups of dust suppressants depend heavily on air humidity level. Magnesium
chloride attracts and retains moisture at a relative humidity equal to or greater than 32% (at
25°C), whilst calcium chloride needs at least 29% relative humidity (at 25°C).
Water sprays
Water sprays are often used to control respirable dust in underground mining. Advances in
each of this area can contribute to the reduction of silicosis in the South Africa mining
workforce, silicosis occurs through exposure to crystalline silica dust, consisting of airborne
dust particles less than 10 µm in size.
Different water sprays will be evaluated for their airflow induction and airborne respirable dust
capture capabilities on crystalline silica. According to NIOSH mining, water sprays with
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specific properties are used for airflow induction and airborne dust capture and applying them
to appropriate situations can lead to lower exposures to silica dusts and thereby lower the
occurrences of silicosis. Optimum parameters for the type of spray, water pressure, type of
additive will be determined. (Majee, 2001)
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