physico-chemical characteristics of wastewater from a ball ......physico-chemical parameters –...

Key words: amalgamation, heavy metals, physico-chemical parameters, SSGM, wastewater

Physico-chemical Characteristics of Wastewater from a Ball Mill Facility in Small-Scale Gold Mining Area

of Paracale, Camarines Norte, Philippines

1Department of Science and Technology - Philippine Nuclear Research Institute, Commonwealth Ave., Quezon City, Philippines

2Environmental Engineering Graduate Program, College of Engineering, University of the Philippines - Diliman, Quezon City, Philippines

Jessie O. Samaniego1,2,* and Maria Antonia N. Tanchuling2

Small-scale gold miners in Paracale, Camarines Norte use amalgamation process to recover gold from mined ores. In the process, they dispose untreated wastewater to water bodies. In this study, wastewater from an active SSGM ball mill facility in the area was analyzed for physico-chemical parameters and heavy metal concentrations. A total of 40 samples were gathered from the ball mill facility while in full operation and were analyzed for heavy metals (As, Ba, Cd, Hg, Pb). Results showed that all metals (except for Ba) exceed the effluent regulatory limits including Hg (0.1768 mg/L) and Pb (9.3821 mg/L), which are 44 and 94 times higher than the limit, respectively. Presence of Hg concentration in the wastewater confirms the miners’ illegal use of Hg in amalgamation process. Based on the mercury balance in amalgamation, around 16.8% of total Hg input goes to the sediment and some 0.21% mixed with wastewater and the bulk 82.99% is in the form of amalgam that becomes Hg vapor after burning. Physico-chemical parameters – temperature, pH, and true color – are within their respective effluent regulatory limits for Class C waters, while TSS (3,596.9 mg/L) is 36 times higher than the 100 mg/L limit. Other parameters, though not regulated, such as ORP (343.9 mV), turbidity (> 800 NTU), and apparent color (9,880 PCU) were analyzed with high concentrations. From this study, wastewater treatment is recommended before disposing of to the receiving waters to reduce the concentration of heavy metals and TSS. Also, the full and strict implementation of the people’s small-scale mining law must be maintained to protect human health as well as the environment from the adverse effect of the use of Hg in SSGM processes.

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Philippine Journal of Science147 (3): 343-356, September 2018ISSN 0031 - 7683Date Received: 15 Aug 2017

*Corresponding author: [email protected]

INTRODUCTIONSmall-scale gold mining (SSGM) plays an important role in poverty alleviation in the rural communities, especially in the developing countries including the Philippines. It is a source of livelihood of at least 10-20 million people worldwide (Telmer & Veiga 2008), while the International Labor Organization (ILO) extrapolated that 80-100 million

people worldwide are directly and indirectly dependent on this activity for their livelihood (Hinton et al. 2003; Hentschel et al. 2003). As the price of gold continues to rise, the SSGM activities around the world also continue to grow. In effect, the demand for mercury (Hg), which is being used in amalgamation process in many SSGM areas, is also increasing and currently it represents 1/3 of worldwide Hg consumptions (Telmer & Veiga 2008). Mercury is one of the most toxic heavy metals released in the environment and its major effects to humans include

Philippine Journal of ScienceVol. 147 No. 3, September 2018

Samaniego & Tanchuling: Physico-chemical Characteristics of SSGM Ball Mill Facility Wastewater in Paracale, Camarines Norte

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Table 1. Salient features of small-scale mining in the Philippines.

Revised Implementing Rules and Regulations of the “People’s Small Scale Mining Act of 1991”

Small-scale mining area Declared as People's Small-Scale Mining Area or Minahang Bayan with a minimum land area of 20 hectares

Investment <Php 10,000,000.00 during the entire term of the small-scale mining contract

Small-scale miners/contractor

Filipino citizens; registered on Provincial/City Mining Regulatory Board; and under a small-scale mining contract

Small-scale mining contract area

1.25-20 hectares as determined by Provincial/City Mining Regulatory Board

Amount of ores to be extracted and disposed of

<50,000 metric tons annually

Mineral processing Centralized custom mill

Mercury use Not allowed

Environmental protection Comply with the applicable rules and regulations on environmental protection and conservation

Sale of gold Sold to Banko Sentral ng Pilipinas (Central Bank of the Philippines)

Tax Pay all fees, taxes, royalties, or government production share

Reporting Monthly production report and annual financial report

neurological and renal disturbances and impairment of pulmonary function (Al-Garni et al. 2010).

In 1984, small-scale mining (SSM) including SSGM in the Philippines has been defined from the Presidential Decree 1899 as a single unit mining operation using manual labor on open cast or shallow underground mining, without the use of sophisticated mining equipment, and having an annual production of not more than 50,000 metric tons of ore (MNR 1984). The law aimed to give livelihood to the underprivileged Filipinos especially those who are living in the rural and mountainous areas. Small-scale miners began to use mercury, cyanide, and other toxic substances in the mining processes as these materials were not then regulated by the government. Earliest reported study on the use of amalgamation of gold ore with Hg in ball mills in the Philippines was in mid-1980s at Diwalwal in Mindanao (Appleton et al. 1999). In 1991, the enactment of the People’s Small Scale Mining Act (RA 7076) repealed/revoked PD 1988. The law was an effort to create more work opportunities and provide sustenance to small-scale miners in the country (DENR 1992). Under this law, small-scale miners were required to form into cooperatives to be awarded with the mining contract and for proper technical control and supervision by the DENR. The use of mercury, cyanide, or any other toxic substances in any mining processes is under the discretion of the regional DENR office (DENR 1992). In 2015, latest revision of SSM law (RA 7076) in the Philippines took effect, where a total ban on the use of mercury was implemented in any phase of SSGM processes and gold extraction must be undertaken only via centralized custom mills located in mineral processing zones (DENR 2015). Other important features of SSM in the Philippines includes investment, amount of ores to be extracted, sale of gold, tax, etc. are listed in Table 1.

From mid-1980s, most of the small-scale miners in many areas in the Philippines used amalgamation to extract gold from the mined ores (Israel & Asirot 2002; Velasquez-Lopez et al. 2010; Cortes-Maramba et al. 2006; Appleton et al. 1999). In amalgamation process, Hg is used to recover free gold from primary ores to form amalgam, which eventually being burnt to evaporate Hg and collect the gold (Israel & Asirot 2002; Cortes-Maramba et al. 2006). Burning of amalgam emits vaporized Hg that adds to the contamination of workers and populace in the community, as it travels long distance in the atmosphere and eventually settles and mixes with the rain going back to the water bodies, where it is converted to methylmercury (MeHg) in the sediment by microorganisms. This method is commonly used in gold-rush areas by small-scale miners because of its simplicity in applications and requires relatively low investment (Israel & Asirot 2002; Hinton et al. 2003). In the milling and panning processes, tailings and wastewater generated contain high concentrations of

suspended solids and heavy metals, including Hg. Most miners dispose of wastewaters directly into the rivers and creeks with a simple sedimentation tank in the ball mill facility as their treatment process. This practice contribute to the pollution of the environment and pose health risks to miners and other people living in the mining area (Velasquez-Lopez et al. 2010).

In 2000, the estimated consumption of Hg used in various SSGM sites in the Philippines was 10,000-30,000 kg/yr (Veiga et al. 2005; Pirrone & Mason 2009) and it was released in different pathways such as sediments, wastewater, and vapor. Previous studies were conducted to assess and document the extent of contamination of Hg from SSGM operations at different mining areas in the Philippines. In Ambalanga Catchment in Benguet, the concentration of total Hg in stream sediments is ranging from 1.18 to 2,600 ng/g, while MeHg concentration was detectable only in sediments and constitute 0.1-3% of the total Hg in sediments (Corpus et al. 2011; Maglambayan et al. 2005). The rice paddy field soils irrigated by river from mining site in Monkayo near Mt. Diwalwal in Mindanao has an average of 24 mg/kg of Hg, while in downstream river of Diwalwal is characterized with extremely high



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Table 2. Hg concentrations in the surface water and sediments near ball mill facility in Paracale, Camarines Norte (Samaniego et al. 2014).

Description of StationWater samples

(mg/L)Sediment

samples (mg/kg)

Pond (2 m from ball mill) 0.00054 10.94

Paddy field (10 m from ball mill)

0.03889 1.49

Tap water (within the ball mill)

0.0000111 --

Gumaus River 0.00196 4.44

Gumaus River mouth to Pacific Ocean

0.00069 0.15

levels of Hg of both in water (maximum 2,906 µg/L) and in bottom sediments (>20 mg/kg) (Appleton et al. 1999). In Apokon, Tagum, Davao del Norte, Hg in sediments ranged from 0.553 to 66.471 µg/mg (d.w.), while water samples from river systems 15 km from mining site exhibited mercury levels of 72.8-78.4 ng/mL (Akagi et al. 2000).

In Gumaus village in Paracale, Camarines Norte, Hg concentrations present in the surface water and sediment samples from pond, paddy fields, and at the mouth of the river near the sea as well as tap water from the faucet where the process water is sourced (Table 2) were reported by Samaniego and co-authors (2014). The nearby Malaguit River in Paracale was monitored by Environmental Management Bureau (EMB) during 2006-2013; total mercury (THg) concentrations ranging 3-6 µg/L was measured in 6 out 70 sampling events. These Hg concentrations measured in land and water bodies are believed to be coming from the wastewater discharges of ball mill facilities in the area. Perez and Appel (2007) estimated that there are about 50 ball mill facilities in the area and releases 750-1500 kg of Hg per year. Initial assessment on the human health exposure of Hg among workers and residents near the ball mill facility in Paracale showed a range of 1.27-16.21 μg/g of total Hg present in hair samples (Diola 2014), which are below the no observed adverse effects level (50 μg/g) of World Health Organization (WHO).

Other heavy metals present in the wastewater such arsenic (As), barium (Ba), cadmium (Cd), and lead (Pb) were also considered in this study as their respective concentration are regulated by the DENR. Ba and Pb can be traced from the chemical composition of mined ores and rocks in the gold mineralized area of Paracale (Giese et al. 1986), while Cd could be caused by leaching from the parent rock. Paracale and its neighboring town Jose Panganiban in Camarines Norte has a reported mineral reserves of

Fe, Pb, Zn, Ag, and Au (EMB-Region 5 2004). While in the nearby Larap-Paracale mineralized district, high concentration of Pb was measured in the soil and rock samples (65-190 mg/kg) and tailings (11,460 mg/kg) (Vargas et al. 2016). Arsenic is known to be commonly associated (Au-As) with gold deposit, where a quasi-steady As-bearing pyrite extracts solid solution Au from hydrothermal fluids through absorption (Zhu et al. 2011). In the assessment of the presence of As in Paracale mining district, it indicates that it may threaten the aquatic life and plants of the surrounding areas (Tetra Tech 2001).

Despite the number of studies carried out to measure the concentrations of Hg and other heavy metals present in the surface water bodies and sediments near or within the SSM areas in the Philippines, the evaluation of the wastewater quality from the ball mill facilities is still poorly documented. The objective of this study is to provide an assessment of the physico-chemical characteristics of the wastewater from ball mill facility that uses Hg in amalgamation process in gold extraction. Although the use of Hg is not allowed in any phase of gold extraction in the country, there are still reports that small-scale gold miners still use Hg especially in those areas where there are no declared People's Small-Scale Mining Areas. The present study will likewise quantify the amount of Hg used by miners in extracting gold from ores based on its concentration in the wastewater. Other physico-chemical characteristics of the wastewater coming out from ball mill facility will also be evaluated in accordance with the limits stated in the Philippine effluent standards (DAO 2016-08) for Class C waters.

MATERIALS AND METHODS

Study Area The study was conducted in a SSGM area of Paracale, Camarines Norte (Figure 1). It is located 320 km south of Manila. The municipality of Paracale is located in mountainous area where houses, mainly wooden huts, tunnels, ball mill facilities and shops are mixed together. The area has a tropical climate and it experience rainfall throughout the year, even during dry season. Rivers and estuaries in the area are classified as Class C which can be used for the propagation of and growth of other aquatic resources, and utilized for agriculture, irrigation and livestock watering. The Paracale mineralized district has a positive ore reserve ranging from 3.10 – 13.45 g Au per ton of ore (EMB-Region 5 2004). Mining practices in the area include sinking tunnel and underground mining and there are rampant underwater and open pit mining (Soriano 2012). There are no organized miners’ cooperative in the study area and was not declared as



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Figure 1. Map of Camarines Norte province showing Paracale town as the study area.

People’s Small-Scale Mining Area, hence the mining operations were believed to be illegal, especially on using Hg in extracting gold by amalgamation process. Water samples were collected from the tailings collection tank of an active ball mill facility in Gumaus village in Paracale (14°17’47.04”N, 122°43’47.46”E). The selected ball mill facility accepts ores from the miners of Gumaus and villages of neighbouring town Jose Panganiban. It operates daily and release wastewater on a continuous basis.

Use of Mercury in Amalgamation ProcessA ball mill drum being used in amalgamation process has a dimension of 0.6 m diameter and 1.0 m long and can accommodate up to 100 kg of crushed ores in one batch of milling and amalgamation. A typical amalgamation process in a ball mill facility in Paracale, Camarines Norte is shown in Figure 2. It starts with the manual crushing of the gold ores to separate particles into desired size of

ores then fed into the ball mill, mixed with water and lime, and undergoes milling. After 1 h, Hg is added to the ball mill and undergo further mixing for another 1 h to allow gold attach to the Hg. The formed amalgam is then separated and placed in a basin for settling. Further washing is done by applying more water to the milled ore to remove slurries and leaving only the fine amalgam. The amalgam is then squeezed using fine cloth to remove the excess Hg. Borax (Na2B4O7·10H2O) is added to further refine the amalgam by removing the impurities. After cleaning, the amalgam is ready for blowtorching to burn the Hg and collect the sponge of gold.

The tailings collection tank has a dimension of 3 m long and 1 m width with a depth of 1.5 m. With an estimate of 1 m3 of contaminated process water and 0.35-0.40 m3 solids from the ball mills that flow into the tailings collection tank daily, it will be in full capacity in two weeks. Wastewater overflows from the tank and goes



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Figure 2. Diagram of the amalgamation process in small-scale gold mining.

to the receiving water body while the sediment is being collected and brought to the large scale operator in the area to undergo further gold extraction using leaching with cyanide. However, these sediments from ball mill still contains considerable amount of Hg and other heavy metals, which are still present in the tailings from leaching process of cyanidation.

Assessment of Mercury EmissionsMercury emissions in amalgamation process were assessed by actual observations and interviews with the operators and owner of the facility. The initial amount of Hg and crushed ores were determined by weighing before placing inside the ball mill before milling. After the milling, samples were gathered from the sediment and wastewater and it analyzed using cold vapor AAS to determine the Hg concentration. The measured Hg concentration of sediment and wastewater from ball mill and panning were used to calculate the total amount of Hg present in sediment and wastewater, respectively. The amount of Hg in amalgam that will undergo blow torching was then estimated by subtracting the calculated amount of Hg from sediment and wastewater.

Sampling and Analyses of WastewaterThe outline of experimental design of the present study is shown in Figure 3. Exploratory phase conducted in Dec 2009 to determine the heavy metal concentrations in different sites (Figure 4) which include ball mills, creeks, rivers, estuaries and sea within the SSGM area in Paracale, Camarines Norte (Samaniego et al. 2013). In four out of 11 sampling sites, heavy metals were found in water, while heavy metals in sediment samples found in two sites (Table 3). Concentrations of heavy metals were not present in water samples from Sites 2, 5, 6, 7, 8, 9, and 10. Sites 3 and 4 are active ball mill facilities with identical

ball mills being used in amalgamation. One of these active facilities (Site 4), located at Gumaus village in Paracale, was selected to be study site where the entire wastewater samples from succeeding sampling events were collected.

Water samplings from the selected ball mill facility were conducted from Dec 2009 to Sep 2014 and divided into two periods. The first sampling period was conducted from Dec 2009 to Apr 2013 by random sampling technique to test the effect of different activities in the ball mill facility during sampling. In this period, only heavy metals (As, Ba, Cd, Hg, Pb) were analyzed from the samples gathered from the outlet of tailings collection tank (Figure 5) for five sampling days with different observed activities (cleaning, repair, no operation, and full operation) in the ball mill facility during sampling visits.

The second sampling period was conducted from Dec 2013 to Sep 2014 with five sample gathering events while the ball mill was in full operation. Each sampling event lasted for two days and gathered eight samples in each event for a total of 40 samples in the whole period. In this period, wastewater samples were tested for heavy metals and 11 physico-chemical parameters, namely temperature, pH, oxidation-reduction potential (ORP), electrical conductivity (EC), turbidity, dissolved oxygen (DO), total dissolved solids (TDS), salinity, total suspended solids (TSS), and color (true and apparent). The physico-chemical parameters – temperature, pH, ORP, EC, turbidity, DO, and TDS – were measured on site using Horiba Multi Water Quality Checker U-5000G (Japan) from 9:00 AM to 2:00 PM, while TSS and color of water were analyzed in the laboratory. Wastewater samplings were done between 9:00 AM and 2:00 PM in every visit to the ball mill facility. Samples were collected from the outlet of tailings collection tank inside the facility and were placed in 1000-mL polypropylene bottles and



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Figure 3. Outline of experimental design of the study.

Figure 4. Sampling sites in Gumaus village, Paracale, Camarines Norte during exploratory phase.



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Table 3. Heavy metal concentrations of water and sediments from selected sampling sites during exploratory phase. (Samaniego et al. 2013).

Heavy Metals Water Samples (mg/L) Sediment Samples (mg/kg)

Site 1 Site 1.1 Site 3 Site 4 Site 2 Site 3

Arsenic (As) 0.009 0.208 0.272 2.287 ND 0.015

Barium (Ba) ND 1.95 2.01 11.23 ND 0.98

Cadmium (Cd) ND 0.031 0.104 0.034 ND 0.018

Mercury (Hg) 0.075 0.102 0.397 0.126 ND ND

Lead (Pb) 0.09 3.56 16.77 26.91 0.06 17.63

Detection limit for As, Ba, Cd, Hg and Pb are 0.001 mg/L, 0.2 mg/L, 0.003 mg/L, 0.0001 mg/L and 0.01 mg/L, respectively.

Figure 5. Ball mill facility where the wastewater samples gathered.

brought to the laboratory for TSS and color of water tests. Total suspended solids were measured at the University of the Philippines - Environmental Engineering laboratory using gravimetric method and dried at 105°C. Apparent color of water was measured employing colorimetric platinum cobalt method using Hanna Color of Water meter (USA), while true color was measured after the water samples were filtered using Whatman GF/F fiber membrane filter.

Separate water samples were placed in 1000-mL bottles and placed in a container with ice for sample preservation during transport from the site to laboratory for heavy metal analyses using Atomic Absorption Spectrophotometer (AAS), following appropriate method suggested by APHA-AWWA Standard Method for the Examination of

Water and Wastewater (1998). Hydride generation AAS was used for As, flame AAS for Ba, Cd and Pb, and cold vapor AAS for Hg. The limit of detection for the method used in analyzing the metals are 0.001 mg/L for As, 0.2 mg/L for Ba, 0.003 mg/L for Cd, 0.01 mg/L for Pb, and 0.0001 mg/L for Hg. Results of the measured physico-chemical parameters and heavy metals were compared to the government effluent limits stated in DAO 2016-08, while the presence of Hg in wastewater will confirm the extent of miners’ illegal use of Hg in gold extraction by amalgamation process.

Settled sediment from the bulk of SSGM wastewater from Paracale was collected and analyzed for heavy metal concentrations using acid digestion (As, Ba, Cd, and Pb) and following US EPA Method 245.5 for Hg then



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measured using hydride generation AAS for As, flame AAS for Ba, Cd and Pb, and cold vapor AAS for Hg.

RESULTS AND DISCUSSION

Mercury Emissions to the EnvironmentA ball mill in the facility where the samples gathered can accommodate up to 100 kg of crushed ores in one batch of milling together with water (40-50 L) and around 6-8 g of Hg. Aside from tailings collection tank that also serves as settling tank, there were no other treatment processes employed in the ball mill facility so Hg is mixed with water and distributed to the different pathways such as sediments, wastewater, and in the air (Figure 6). By calculating the amount of crushed ores (100 kg) loaded in the ball mill multiplied by the average Hg concentration in the sediment (11.70 mg/kg), the amount of mercury went to the sediment was 1.18 mg or around 16.8% of total mercury input. The Hg concentration in water (0.18 mg/L) multiplied by amount of water consumed during milling and panning (around 90 L) gives 0.015 g of Hg present in the wastewater, which was around 0.21% of the total Hg input. The bulk of the total mercury input in the process was in the amalgam (82.99%) that eventually transform to mercury vapor (Hg0) after burning. The amount of Hg that goes to the tailings (sediment and wastewater) was lower than the Hg in tailings (27.48%) from the Hg balance for amalgamation of the whole ore in ‘‘Chancha’’ processing centers study in Ecuador (Velasquez-Lopez et al. 2010). In the same study, excess Hg (58.33%) during squeezing is being recovered while 14.19% is evaporated during burning compared to the

whole amalgam burning in Paracale that evaporates 82.99% of the total Hg input.

Hg in the wastewater travels downstream and dispersed to a wide area of bodies of water, where it can transform into methylmercury (CH3Hg+) in the sediments of lakes and rivers and finally in the sea. Methylmercury can be transferred and concentrated in fish (UNIDO 2006) that pose high health risk to people living nearby mining areas for possible consumption of Hg contaminated fish. Mercury vapor can easily be transferred to the miners through inhalation or simply attached to the body. It may also travel long distances in the atmosphere and eventually come down with the rain and mix with the surface waters and transformed into MeHg by microorganisms.

First Sampling PeriodThe result of heavy metal analyses, its corresponding effluent limits, and the activities in the ball mill facility during sample gathering in the first period are presented in Table 4. Background concentration of Hg can be traced from the concentration of Hg in tap water (0.01 µg/L) used as input to the amalgamation process, since there was no reported Hg concentration found in the chemical composition of rocks in Paracale mining district. The use of Hg in amalgamation process has direct impact on the wastewater as elevated concentration of Hg were measured from the wastewater samples gathered from ball mill facility. The concentrations of other metals (As, Ba, Cd, and Pb) considered in the study came from the ores mined from mineralized district of Paracale and surrounding areas (Giese et al. 1986; EMB-Region 5 2004; Vargas et al. 2016; Tetra Tech 2001).

Figure 6. Mercury distribution in amalgamation process at SSGM in Paracale, Camarines Norte.



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Variations in the concentration of heavy metals in each sampling dates can be attributed to the activities in ball mill facility during water sampling. In Dec 2009 sampling, the ball mills were operational and the wastewater was continuously flows to the tailings collection tank. In the three sampling events in 2012, various activities were observed in the ball mill facility during the gathering of water samples. For instance, in May 2012, samples were gathered while workers were cleaning the equipment. It was observed that as they were cleaning, the tap water continuously flowed from the faucet, thus diluting the concentration of heavy metals in the collection tank. In Oct 2012 sampling, there were no milling operations and the workers were cleaning the facility using tap water, while in Nov 2012 there were repair works going on and there was no milling operation. In these sampling days, the concentration of the heavy metals decreased due to the additional tap water which entered the collection tank and mixed with tailings, hence reducing the concentration of heavy metals in the wastewater. Samples tested in Dec 2009, showed that there was high concentration of As, Hg, and Pb that exceeds the government effluent limits. These results were also observed in Apr 2013 sampling where all concentration of heavy metals did not meet its respective effluent limits. However, during the three sampling in 2012, ball milling activities were intermittent, and did not

produce wastewater that contains heavy metals except for Hg (10.34 mg/L) in May 2012. High Hg concentration was also measured in Oct and Nov 2012 at 1.14 mg/L and 0.0279 mg/L, respectively that exceeds the effluent limit of 0.004 mg/L. These show that significant amount of Hg from the amalgamation process are mixed with the wastewater and attached to suspended solids and overflows from the collection tank then goes directly to the creeks and rivers in the area. This result further confirms that the miners used Hg in amalgamation in this period, where the use of mercury in gold extraction process was still with the discretion of the regional DENR office (DENR 1992).

Second Sampling PeriodHeavy Metal Concentrat ions. The measured concentrations of the heavy metals in the wastewater for the second sampling period (Dec 2013 to Sep 2014) are presented in Table 5. Heavy metals including Hg concentrations were compared to regulated effluent limits for Class C waters (DENR 2016). Hg concentration in the wastewater serves as confirmatory data on the extent of Hg usage by the miners in the extraction of gold in this SSGM area. The average concentration of As (0.1915 mg/L) is higher than the effluent limit of 0.04 mg/L, with a maximum concentration measured at 0.74 mg/L. Barium concentrations in this period were not detected

Table 4. Concentration of heavy metals of SSGM wastewater in the first sampling period.

Sampling Day Arsenic (As), mg/L

Barium (Ba), mg/L

Cadmium (Cd), mg/L

Mercury (Hg), mg/L

Lead (Pb), mg/L

Activities in the ball mill facility during sampling

5 Dec 2009 2.287 11.23 0.034 0.1255 26.91 On going operation

11 May 2012 0.147 <0.20 <0.003 10.34 0.4141 Cleaning

14 Oct 2012 0.049 <0.20 <0.003 1.14 0.0263 No operation/cleaning

17 Nov 2012 0.007 -- -- 0.0279 3.94 Cleaning/ repair works

6 Apr 2013 0.831 7.63 1.01 0.46 48.97 Ongoing operation

DAO 2016-08 limits 0.04 6.00 0.01 0.004 0.10

Note: Heavy metals Ba and Cd were not included in 17 Nov 2012 sample analysisDetection limit for As, Ba, Cd, Hg, and Pb are 0.001 mg/L, 0.2 mg/L, 0.003 mg/L, 0.0001 mg/L, and 0.01 mg/L, respectively.

Table 5. Concentration of heavy metals of SSGM wastewater in the second sampling period (n=40).

Heavy Metal Unit Mean (Range) St. Dev. DAO 2016-08 Limits

Arsenic (As) mg/L 0.1915 (0.0078-0.742) 0.1456 0.04

Barium (Ba) mg/L <0.20 -- 6.00

Cadmium (Cd) mg/L 0.0073 (0.003-0.021) 0.0049 0.01

Mercury (Hg) mg/L 0.1768 (0.01-0.6371) 0.1526 0.004

Lead (Pb) mg/L 9.3821 (0.52-28.66) 7.5196 0.10

Detection limit for As, Ba, Cd, Hg and Pb are 0.001 mg/L, 0.2 mg/L, 0.003 mg/L, 0.0001 mg/L and 0.01 mg/L, respectively.



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at 0.20 mg/L detection limit of AAS. The range of Cd concentrations of the entire sample is 0.003-0.021 mg/L, with an average of 0.0073 mg/L, which is higher than the regulated limit of 0.01 mg/L. Lead concentrations of the sample tested ranges 0.52-28.66 mg/L with an average of 9.38 mg/L, which is 94 times higher than the effluent limit of 0.1 mg/L. This concentration of Pb measured in all samples can be attributed to the high Pb concentration of soil and rocks mined in the area, as reported in the study of Vargas and co-authors (2016). These heavy metals go to the rivers and lakes and eventually settle in the bottom of the water bodies as there is no treatment process in the facility to capture these metals. The analyzed concentrations of Hg in this period were all above the effluent limit, with concentration ranging 0.01-0.6371 mg/L and with an average of 0.1768 mg/L or 44 times higher than the limit of 0.004 mg/L. This elevated concentration of Hg in the wastewater can be accounted from the 0.21% of the initial amount of Hg added in the ball mill during amalgamation process. High concentration of Hg and Pb may bioaccumulate in fishes and other local biota and if eaten by people, may cause harm to those living in the area. Heavy metal concentrations of the SSGM wastewater tested in this study ranked as Pb>Hg>As>Cd>Ba. Continuous loading of this type of wastewater for long period of time will give a long term impact on the receiving water bodies, soil, and in the food chain.

The high concentration of Hg in the wastewater from ball mill facility can be traced from the uncontrolled and illegal use of Hg in amalgamation process, which the local DENR regional office had the discretion on the use of Hg in any mining processes during the conduct of this study. This situation, however, can be corrected by strict

implementation of the revised rules and regulations on RA 7076, wherein the use of Hg in any mining processes is not allowed in SSGM. The DENR, as the regulator, should take into account the prohibition of entry of Hg in the SSGM area. In addition, miners should urge to shift into an alternative, non-Hg method of extracting gold. Heavy metals present in the wastewater can be reduced to meet the effluent limits by installing properly-designed sedimentation tanks which can prolong the travel of water while the suspended particles are settling. Heavy metals can also further reduce the concentration or even recover using on-site wastewater treatment system such filter bed with low cost plant derived biomass as adsorbent.

Physico-chemical Characteristics. The means, ranges, and standard deviations of the measured physico-chemical parameters of the SSGM wastewater are presented in Table 6. Out of 11 effluent physico-chemical parameters analyzed in this study, four (temperature, pH, TSS, and true color) are regulated in the Philippines (DENR 2016).

Water temperature in the collection tank measured by water quality meter has a range of 24.29-30.20°C. These values are within the effluent regulated water temperature (25-31°C) for Class C waters. There was no temperature rise measured from the water samples and it remained within the required range since there was no heating and boiling in amalgamation process, hence it will not affect chemical and biological reactions taking place in water for fish and other aquatic living organisms.

Measured pH values of the wastewater ranged 6.17-8.17 with an average of near neutral (6.87) and are within the regulated effluent pH limits of 6.0-9.5. These pH values cannot affect the growth and propagation of fish and other aquatic resources. The near neutral pH of the effluent is

Table 6. Physico-chemical characteristics of SSGM wastewater in the second sampling period.

Heavy Metal Unit Mean (Range) St. Dev. DAO 2016-08 Limits

Temperature °C 27.22 (24.29-30.20) 1.3206 25-31 (a)

pH (range) Unit 6.87 (6.17-8.17) 0.4661 6.0-9.5

Oxidation-Reduction Potential mV 343.9 (241-425) 44.2507 --

Electrical Conductivity mS/cm 0.1283 (0.065-0.215) 0.0433 --

Turbidity NTU >800 -- --

Dissolved Oxygen (min) mg/L 5.55 (4.25-7.52) 0.7638 --

Total Dissolved Solids g/L 0.0834 (0.042-0.139) 0.0282 --

Salinity ppt 0.055 (0-0.1) 0.0497 --

Total Suspended Solids mg/L 3,596.9 (510-13,791) 3,420.57 100

Color (True) PCU 45 (0-60) 20.49 150

Color (Apparent) PCU 9,880 (6,720-11,200) 1,925.57 --

Note: (a) The value is based on water quality guidelines for freshwater Class C rivers.



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due to the application of lime in the amalgamation process, which neutralizes the acidic water generated from the decomposition of ores (de Beer et al. 2008). The same near neutral pH value was reported from the characterization of gold mine wastewater in Ghana (Acheampong et al. 2010).

Oxidation-reduction potential of the wastewater tested ranges 241-425 mV, which indicate that the entire wastewater samples has high oxidizing agent such as oxygen. ORP is found to be temperature-dependent, therefore a rise in temperature will cause to increase the oxidizing agents in the water.

Electrical conductivity, which is the capability of water to carry electric current and is related to the dissolved minerals present in the wastewater, has measured value ranges 0.065-0.215 mS/cm with an average of 0.1283 mS/cm. Although EC is not regulated, these values are lower compared to the reported EC values (0.6-10 mS/cm) from different types of mining wastewater (Dharmappa et al. 1995; Acheampong et al. 2010). Electrical conductivity is related to total dissolved solids (TDS) since these are the sum of all ionized solutes and its direct relationship in wastewater samples has been established in previous correlation studies and rough estimation. The measured TDS values ranging 0.042-0.139 g/L with an average of 0.08345 g/L are also lower than the typical gold mine effluent TDS concentration of 2.9 g/L (Acheampong et al. 2010). Salinity, like EC and TDS, is the total concentration of electrically-charged ions present in the wastewater (Bhatnagar & Devi 2013). Level of salinity is not regulated in the Philippines but high concentration of it would have an impact on aquatic ecosystems. Previous studies demonstrated high positive correlations among these three parameters, which were influenced by the presence of suspended minerals such as carbonate, bicarbonate, chloride, sulfate, phosphate, nitrate, calcium, magnesium, sodium, and others ions that cause TDS, EC, and salinity to rise.

The entire wastewater samples have high turbidity at >800 NTU. Though turbidity is not regulated, high turbid water contains a lot of particles suspended that affected its clarity. The measured TSS range is between 510 mg/L and 13,791 mg/L with an average of 3,596.90 mg/L. These values are almost 36 times higher than the regulated limit of 100 mg/L for Class C waters. Effluent with high concentration of suspended solids has an impact on surface water quality as it adsorb and concentrate trace metals and other contaminants and settle in the bottom of the creek or river.

The effluent of SSGM facility release wastewater with DO concentration range from 4.25 mg/L to 7.52 mg/L with an average of 5.55 mg/L, which is near the 5.0 mg/L minimum DO level needed for production and spawning

of fish (Bhatnagar & Devi 2013). These low DO values are expected since the solubility of atmospheric oxygen varies with the temperature of the water, which in this study is relatively high (24.29-30.20°C). It also explains that warmer surface water requires less dissolved oxygen to reach full air saturation.

The measured apparent color of water ranged from 6,720 PCU to 13,760 PCU with an average of 9,880 PCU, but the true color of water after the removal of colloidal or suspended particles has an average of 45 PCU which is lower than the regulated true color of 150 true color units. High values of apparent color of water measured in this study was due to the high turbidity of the water samples in which suspended colloidal particles present in the water samples can alter the observed color.

In general, the physico-chemical characteristics of the wastewater from ball mill facility in the area are not acceptable for Class C water bodies, especially TSS, turbidity, and apparent color. This type of water cannot be used for the propagation of fish and other aquatic resources, boating and fishing, and likewise not good for agriculture, irrigation, and livestock watering. In order to meet the effluent limit, treatment of wastewater is needed. Sedimentation tank can be designed properly to reduce significant amount of TSS, turbidity as well as color before disposal to water bodies. Installation of on-site wastewater treatment system next to sedimentation tank such as filter bed can further capture the suspended solids and other particles in the substrates.

Heavy Metal Concentrations of Sediment. The heavy metal concentrations of the sediment settled from SSGM wastewater samples are presented in Table 7. These high concentrations of heavy metals indicate that the ions settle together with the suspended solids and physically entrapped to the sediment. High Pb concentration is in agreement with the Pb concentrations measured from the soil, rock, and tailings samples from Larap-Paracale mining district (Vargas et al. 2016). Hg concentration in sediment was directly related to the use of Hg in amalgamation, while other heavy metals (As, Ba, Cd) were traced from the composition mined ores in the area. When miners collected the sediments from the tailings collection

Table 7. Heavy metal concentrations of sediment settled from SSGM wastewater (n=3).

Heavy Metal Unit Concentration

As mg/kg 39.31

Ba mg/kg 168.55

Cd mg/kg 6.52

Hg mg/kg 11.69

Pb mg/kg 4,157.66



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tank and brought to the large-scale gold extractor using cyanide, these heavy metals may still be available in the tailings being disposed of to the tailings pond and it may eventually return to the ground. Hg in tailings will undergo methylation and transform to MeHg, which when leached out to water bodies may be transferred and concentrated in fish and enter the food chain, where it then poses health risk to the people living in the area.

CONCLUSIONS AND RECOMMENDATIONSPhysico-chemical characteristics and heavy metal including Hg concentrations of wastewater from an active SSGM ball mill facility in Paracale, Camarines Norte was presented in this study. High concentration of Hg (0.1768 mg/L) was directly associated from the use of Hg in amalgamation process that are widespread practice in the study area, although the Philippines’ small-scale mining law prevents miners from using Hg any phase of mining processes. Based on the mercury balance in amalgamation process, the pathways of Hg contamination in the environment are as follows: around 16.8% of total mercury input goes to the sediment and some 0.21% mixed with wastewater that travels downstream and dispersed to a wide area of bodies of water where it can transform into methylmercury, while 82.99% is in the form of amalgam that becomes mercury vapor after burning. Aside from Hg, other heavy metals (As, Cd, Pb) in the wastewater are in high concentrations and exceed the government effluent limits, especially on Pb (9.3821 mg/L) which is 94 times higher than the limit.

Out of 11 of the physico-chemical parameters analyzed in this study, four are regulated by DENR (2016) for Class C waters. Temperature and pH are within the regulatory limit, while dissolved oxygen, though not regulated, has measured average that is slightly above the 5 mg/L minimum limit for production and spawning of fish. However, the measured average TSS concentration of 3,596.90 mg/L was around 36 times higher than the regulated limit of 100 mg/L for Class C waters. High concentration of suspended solids has an impact on surface water quality as it adsorb and concentrate trace metals and other contaminants and settle in the bottom of the creek or river. The study also revealed that the effluent is a high-oxidizing agent with an average ORP of 343.9 mV. TDS and EC values in this study are lower compared to the values measured in gold mining effluent in Ghana (Acheampong et al. 2010). Salinity has tolerable value, while turbidity and apparent color, although not regulated, have very high concentrations. The regulated true color of the wastewater is within the effluent maximum limit.

Treatment of such contaminants is recommended before disposal to the receiving waters. Also, mercury-free mining techniques that are safer for miners, their families, local communities, and the environment are hereby suggested to apply in the extraction of gold. The DENR and local government unit must work closely to prevent the entry of Hg in the mining area. Full and strict implementation of Peoples’ Small Scale Mining Act must be maintained (e.g., declaration of more People's Small Scale Mining Area) to create more work opportunities and provide livelihood to small-scale miners in the country. The data presented in this study will serve as the baseline data for researchers and policy makers who are in search of solutions to the environmental challenges brought about by SSGM in the Philippines.

ACKNOWLEDGMENTS The authors acknowledge the Department of Science and Technology - Philippine Council for Industry, Energy and Emerging Technology Research and Development (DOST-PCIEERD) for funding the project, and special credit to the Department of Science and Technology - Engineering Research and Development for Technology (DOST-ERDT) for the scholarship grants and research fund for the study.

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