GOLD MINES AND IMPACT OF HEAVY METALS ON THE ENVIRONMENT

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GOLD MINES AND IMPACT OF HEAVY METALS ON THE ENVIRONMENT

BADER A. HAKAMI

Faculty of Earth Sciences, King Abdul Aziz University, Jeddah, Saudi Arabia

ABSTRACT

This research report puts light on the research and the study of gold mining plant in Oman and its assessment and its contribution of gold mining into various other environmental media on the basis of heavy metals. In this research study, various samples were collected from crop plants, stream waters and soil of the plant area of gold mining. In this research the collected samples were further examined for thirteen heavy metals such as barium (Ba), iron (Fe), strontium (Sr), aluminum (Al), zinc (Zn), lead (Pb), cobalt (Co), cadmium (Cd), copper (Cu),nickel (Ni), manganese (Mn), Chromium (Cr), vanadium (V). During the investigation, the acid evaporation pond, the water showed a high amount of concentration of iron as well as a few of the residual quantities of zinc, vanadium and aluminum, on the other hand water for the citizens showed the concentrations all above Who standards and Omani. The water on the surface area indicated high concentrations of copper and major concentrations of manganese, nickel, aluminum, iron and zinc. Whereas the desert plant species growing nearby the gold pit showed large concentrations of heavy metals such as manganese, aluminum, nickel, iron, zinc as well as vanadium, also some of the other plants of the same desert plant species utilize as a control indicated only a few concentrations of all heavy metals.

After analyzing the whole research study of heavy metals, the researcher discovered that few of the toxic metals engaged by plants showed by restriction of major metal.

Keywords: Gold Mines, Pollution, Heavy metals, mining.

INTRODUCTION

Mining is one of the activities of human that puts a negative impact on the quality of the environment. Mining is the main source of destruction of natural ecosystems that is done by soil and vegetation removal, as well as burial under the waste disposable sites. The wastage in mining can be divided into two categories such as waste rock generated while removing the body of the ore, and mine tailings occurrence in the processed ore doling out. There are many mineral processing methods like ores and rocks, recovery of the ores, disposal of wastewaters and tailings around the ISSN 0976 – 6340 (Print)

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metal mines WHO (2006). The heavy metals are discharged in soil, water and sediment that is also known as environmental media. According to the changes in chemical and physical properties in the Lithosphere, heavy metals in tailings are dispersed, transferred and collected from animals and plants are further passed up on the food chain to the human beings as last and the final consumer. Heavy metals are present in tailings and few toxic and harmful contaminants that are present in the soil that put a harmful effect on the ecosystem near the metal mines. Soil contamination, water and biota by heavy metals, sediments all these are the main concern in the mining sites for the reason of their toxicity, collection of food chains and persistence (Akabzaa & Banoeng,2005). Heavy metals that are connected with mining are of particular attention for various reasons. Heavy metals have a tendency of collection of soils and sediments, also have long persistence time that is not biodegradable.

Another reason is omnipresent in the soils and sediments that come from natural as well as not natural sources inherited from big parent rocks, water applied in local and long range atmosphere with deposition of dust and mining emissions (Sengupta, 2002). These heavy metals enter the food chain followed by human beings, including animals and plants. Heavy metals with low concentrations play an important role as nutrients for animals and plants as well as humans, these are present in the high quantity in different forms which is not only harmful but also put adverse effects.

An example of toxic in high concentration is zinc and copper that are also important for normal metabolic Olade (2009). Human organs can get damaged when the zinc and copper quantities increase, it is very harmful. Lead, cadmium, arsenic causes cancer, metabolic disorders, neural and various other diseases and disorders. Arsenic is amongst the most essential contaminants of drinking water in the world as it is believed to cause kidney problems, urinary bladder, lungs and skin problems. Another heavy metal that is lead is responsible for brain failure, nerve, kidney and liver damage in adults, cadmium causes blood damage, bone, liver and kidney failure in long term exposure. Heavy metals are responsible for oxidative damage in plants, metal stress put harmful effect on the stomatal resistance, chlorophyll fluorescence as well as photosynthesis and reproductive processes lead decreases the production of chlorophyll while arsenic comes in contact with the metabolic processes, hence the growth of the plant is decreased (Adimado & Amegbey,2003). There are ample of case histories that are related with the health problems which are formed due to the adsorption of the heavy metals which were reported and studied from various parts of the world.

Major important issues concerned and connected with the metal mining activities is acid mine drainage. Acid mine drainage is formed by the oxidation of metallic sulphides and pyrite. The origin and the beginning of the major chemical, physical and biological factors of acid drainage are involved in the process which is studied by many investigators all around the world (Meili,2003).

Gold is a precious metal which is found in very small quantities in the gold mines, for this gold mining operations are performed to extract or take out gold in the areas which further results in the environmental damage in geographical term. The procedure of m mining is not easy but a difficult process which releases and produces many other harmful and toxic pollutants (Ogwuegbu &

Muhanga,2005). Mining of gold is not an easy task, it negatively affects the environment and is

harmful to the environment when digging is done for mining of gold, in the deposition of the leftover

residue various chemicals are released which is also harmful (Afal & Wiener,2014).Chemical

processes are formed in the procedure of the gold mining or the process of extraction of gold. The

recent technique used for the extraction of gold from the gold mines is cyanide leaching which

consumes energy as well as water in very large quantity, it also puts in global warming, produces

wastage, discharges hydrogen cyanide. Air pollution, water and land all these are by-products of gold

mining when done with the method or technique of cyanide leaching technique. After the completion

of the process of gold mining often leads to the damage and destruction of the villages and the

communities have to relocate to a new location. Whole landscape gets disturbed by gold mining,

geographical stability gets imbalanced, the water table gets disturbed and the ecosystem. All this is

done because of the procedure of the removal large amount of ore to obtain gold. Water systems and

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underground water get highly disturbed with mining of gold. All the wastage and toxic waste is formed which is very harmful and hazardous for the environment. One more method is used before digging of gold that is blast operation with the help of heavy vehicles which produces heavy noise, and noise results in noise pollution. Mines can be open as well as underground, dust exposure is at the same levels in both (Seyire,2005). This dust is very harmful, the workers who all are involved in the process gets affected. Another pollution is the pollution of land which is the contamination of the land by the wastage and the solid waste materials on land. Land pollution is the most harmful type of pollution for the people who live in those polluted areas or in any particular polluted location. People living on the polluted land, people gets sick, their organs gets damaged which sometimes results in death. Pollution of air is when the toxic chemicals gets mixed and comes in contact in the atmosphere, many harmful gases gets mixed in the environment (Ogwuegbu & Ijioma ,2003). All the harmful gases enter into the atmosphere and cause acid rain, further results in global warming.

Open mining of gold disturbs the water level of the area around the pit because the water in the area of the pit is emptied, and water is extracted and the area is dried to perform the operation. Cyanide is very harmful for the fishes in the water. Open mines are easily polluted and affected badly.

PROCESSING PLANT

At the processing plant, with the technique of cyanide leaching, gold is extracted, in this method ores are crushed and soaked in the solution of cyanide (Tarras & Wahlberga,2001) The procession of ore involves the following steps that are : grinding and crushing of the ore, pumping of the barren to the storage facility of tailings, adding water to form tailings, detaching the metals from carbon with the help of acid wash and cyanide solution, adding carbon to dissolve metals and help in further formation of the tailings, applying the electrowinning in the operation, adding lime to the ore and solution of cyanide to extract gold from the solution, separating and forming metal products in form of bars etc.

These stages in more detailed form is explained here under :

• Grinding and classification of the size of the ore which further transforms into fine particle size (Aas & Breivik,2005).

• Absorbing and discharging procedure is done for the extraction of the precious metals from the rock( Kumar & Abbas,2013).

• Mending of gold for the production of gold bars (Petruzelli, 2011).

PROCESS OF CRUSHING

The process of crushing by putting the ore in the hooper with the help of a loader, with heavy speed and pressure the ore is then drawn towards the feeder and then moves towards the crushing part. After the crushing part is done, then the crushing is moved to the jaw crusher and moved immediately to the ball mill (Saxena & Misra,2010).

PROCESS OF GRINDING AND SIZING

In the process of grinding and sizing, categorization is done on the basis of the procedure of the reduction of the ore to finest particle size. In this method or in this procedure the ore is directly transferred from the jaw crusher to the ball mill. The ball mill has the maximum amount of share in the steel balls which helps in the assistance in the grinding procedure (Flachier & Lanec,2001).

Water is added inside the ball mill and the reduction of the ore procedure starts. Cyclones are formed

after the discharge of the mill, then the cyclone gravity flows backwards for further grinding

procedure, it flows back to the leaching and the absorbing area also on the trash screen as well. For

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obtaining the finest size of the precious metal from the ore, cyanide is required and is responsible totally.

Figure 1: Plant for gold mining PROCESS OF LEACHING, ABSORBING AND FILTERING

Leaching of the tanks and adsorption of the tanks with the cyanide solution is done to help in the dissolving of the gold into the cyanide solution and changing the flow of the solution from the last adsorption tank to the first adsorption tank. Carbon is mixed into the circuit of the tank in the opposite direction so that gold particles move towards the surface of the carbon (Millard &

Neerchal,2001).The barren passes the adsorption tank to the filter needle tank, and then the filter

cake is dropped in the downward direction till the filter press on the ground, the barren slurry is

removed with the help of the front end loader, then it is loaded into trucks and later dumped into tails

dam and the gravity which has been filtered flows till the water process tank.

74 PROCESS OF ELUTION

Figure 2: Open Pit Figure 3: Jaw Crusher

Figure 4: Ball Mill

When the carbon gets loaded with the gold, the air gets lifted with the help of the first adsorption tank, then it is pumped out with the help of the elution circuit, on the place where gold is washed and heated with the help of water, the solution that is washed is then passed to the circuit which is known as electro winning circuit. The carbon that is remained is again charged and activated by washing it with acid and sent backwards to the last adsorption tank( Shrestha &

Kazama,2007). Original photographs of the open pit, ball mill and jaw crusher are shown here under:

MATERIALS AND METHOD Study of the materials and method

Table 1: Sampling Location

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Table 2: Heavy Metal concentration in soil samples

The plant is located in Oman, production of the gold per month is around 20 kg, where the pit is a terrain which is mountainous with raw soil at the bottom of the pit, the raw soil is cut until it reaches the ground water table (Michael,2013). Samples are arranged, collected and studied of different areas which can be easily understood with the table shown below:

SAMPLING AND REAGENTS

Deionised ultrapure water that is 18 ohm-SG water, Germany has been used for mixing samples and standards. Analytical grade is 37 percent HCL ( Aldrich) , nitric acid is 70 percent, (Sigma Aldrich). ICP multi standards 1 and 2 used to make a curve of calibration which helps in quantifying the samples (Park,2013). Microwave oven digestion proves as one of the appropriate tool and technique for the identifying the samples from the complex matrices and is used in digestion of ashed plants as well as samples of the soil. All the samples of soil and ashed plants are digested in Teflon bombs by using the technique of EPA 30508 in microwave oven that is ETHOSEL, Milestone Microwave System USA, on the set program of eight minutes in phase one as well as four minutes in phase two at two hundred degree temperature. The digested samples are filtered with the help of Whatman filter paper which is then transferred to hundred ml volumetric flask (Lanec,2001).

After the collection of the samples, the samples are studied with the help of PerkinElmer Inductively

Coupled Plasma-Optical Emission S spectrometer that is ICP-OES).All the remaining six blanks are

studied along with the samples which do not show any significant considerable or major

contamination ( Aster,2013). The samples of the plant are first air dried up, then grounded with the

help of the sieved and pestle as well as mortar (100 um). The sieved sample is further ashed into the

muffle furnace at five hundred degree temperature. At last acid is digested with the help of ultrapure

hydrochloric Thirthy seven percent as well as nitric acid seventy percent in same proportion in a

microwave oven in both first and second phases (Jung & Myung,1996).

76 DISCUSSION AND RESULTS

Table 3: Concentration of heavy metals in open pit

Table 4: Heavy metal concentration in crop plant

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Table 5: Analysis of well water

Table 6: Analysis of water from acid evaporation and slurry sample

The trace elements are considered for the study of vanadium (V), barium (Ba), Iron (Fe),

Strontium (Sr), Aluminium (Al), Zinc (Zn), lead (Pb), Cobalt (Co), Cadmium (Cd), Nickel (Nil),

Manganese (Mn) and Chromium (Cr) (Pezzarossa & Gorini, 2011).In this research study , the feed

soil of the plant of gold is analyzed for the concentration of metal, which also gives indication of the

higher concentrations of iron that is 1.4 percent, aluminum that is 10.8 percent, manganese that is

0.29 percent and copper that is 0.32 percent, whereas with the lesser concentrations of cobalt, lead,

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vanadium, chromium, zinc and nickel, shown in table 2. The mineral rocks contains appropriate amount of sulphide minerals and pyrites, where sulphide minerals are harmful because they causes oxidation of pyrites with formulation of the acid solutions on heavy metals, heavy metals become highly mobile when acid rain occurs in the particular region. In the table 3, the analysis of soil and water in open pit is shown in which light blue coloured surface water gets collected (Agyemang,2010). There are very high concentrations of copper that is 4.4 percent. Open pit when compared with the metal concentrations of the feed soil also have higher concentrations of cadmium, lead, cobalt and molybdenum. The surface water is of light blue colour with high concentration of copper. High residual concentration of aluminum, manganese, nickel, zinc, iron, cadmium, cobalt and lead has been analyzed. When these metals such as cobalt, copper, lead, cadmium, zinc which contains mine tailings comes in contact of the scarce rain fall water then it causes pollution in the environment. After this process metals are leached out and then moved to downstream where the water washes the tailings (Notman,2014). Whereas the metals become mobile in neutral pH conditions, at that time leaching is accelerated in lower pH conditions for they are formulated in metals solution (Cobbina & Myilla,2013). In table no. 4, analysis of same vegetation has been done where the plants are taken near the gold pit and also the control plant is collected and gathered more closer to the water well of the citizens about hundred meters in the north direction of the mine.

Analysis of the desert plant which is near to the gold pit shows increase in almost all of the trace elements such as ( Fe, Mn, Al, Zn, Cu, Cr, Co, Ba, V, Ni) as well as lead decreases with molybdenum concentrations on comparison with the desert plant (Essumang & Zugle,2010). In the boron plant concentrations showed decrease by 1.77 percent to 0.07 percent when analyzed and comparison performed to control. Even though the plants are collected and selected from the same genus, and the metal immobilization capabilities are dependent on the availability of the metal concentrations present in the soil because it is responsible for the explanation of growth and difference between the metal concentrations (Saxena & Misra,2010). The concentrations of lead around 80 mg Kg-1 has been keenly observed in the tailings with very high levels of lead in the growing plants which are near to the gold mines or near to the gold mining area. The plants which are downstream or little far from the gold mines have very less concentrations of heavy metals. From this research study, it indicates that with the location of the plants, metal rich soils can be identified.

Toxic and heavy metals are present in all the plants but in different quantities and it totally depends on the area. Humans near the mining area can get ample number of health problems and should keep away from such toxic areas. The toxins enter the soil with the medium of heavy rains, then it enters the water table and then it goes to the surface. Toxic metals like lead (Pb) with high concentrations are not only present in the soil but also in the plants and the surroundings as well with the acid evaporation ponds (Akabzaa & Seyire,2005).The soil contains very high amount of the metals which is very harmful in spite of the excessive phytotoxicity presented in the soil (Duffus, 2002). The citizens get water from the water resources which are located near about five hundred to one thousand in the north direction in downstream of the mine which is up to Who standards and also up to the Omani Standards of drinking water. The table number five shows the water samples and its results acquired from the citizens of that location near about five hundred to one thousand meters to the north side of the gold plant (Tetteh & Golow,2010).This water is used in agricultural purposes.

With the change in the chemical as well as change in the physical state the metal contaminants cause

soil substrate as well as ground water pollution which is very harmful. All the heavy metals in

tailings are transported and sent or dispersed to the accumulation of animals and plants and later on

passes from the food chain to the human beings (Thornton & Iain 1996). In the table number six, the

water analysis from the acid evaporation pond indicates and shows how the mining procedure adapts

certain measures to keep away the harmful toxins and prevent environmental pollution. From the

acid evaporation pond, samples are taken of the soil, other samples are taken from the slurry sample

from the tailing dump which are then studied and keenly observed which shows the concentrations of

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the heavy metals such as lead, copper, zinc and copper (Bánfalvi, 2011). All these concentrations of the toxins are transported downstream in the season of rains which are further transferred with the help of human food chain and with the help of plants.

CONCLUSION

The main threat for the environment is the mineralized rocks which are exposed to open pits and also exposed to the waste dumps. The chemistry of water studied in the area indicates that all the materials have very high capacity of generation of acid drainage with the release of harmful elements and other harmful toxins (Ezeh & Chukwu,2011)These harmful elements are ( Pb, Cd, Cu, Cr, Ni).

The high metal waters may contaminate the local groundwater with the help of solubillisation of the metals which are toxicated metals. When the study in the area of the water chemistry performed, then it showed that there is high capacity of acid drainage. The groundwater gets contaminated with these heavy metals which are toxic. As per the standards of the WHO and Omani , the drinking water with such high concentrations aluminum and heavy metals and toxics is very harmful and it must be considered in the future prevention plans ( Banoeng-Yakubo,2005).Tailings are also very injurious to health because of the presence of cyanide and high metal in it. Restriction on such area is must, Contamination of the food chains can be stopped with a check on the presence of human beings or any living beings near the mining area or location. When there is any absence of the toxins in the soil then vegetation is at minimum risk n vice versa.

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