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A Study on Arsenic Sequestration in Gold Mine Wastes
by Marcelle P. Villegas - July 15, 2021
Here is a recent study that investigates the mechanisms of arsenic partitioning into, or out of, streambed sediments downstream of the Porgera Gold Mine in Papua New Guinea. 
Arsenic (As) is a metalloid element with atomic number 33. Arsenic is known to be released in the environment during gold mining activities. Preventing toxic contamination of soil and water in mine sites is important in a mining operation. This is possible with the application of various techniques on effective arsenic sequestration.
A recent study titled “Arsenic sequestration in gold mine wastes under changing pH and experimental rewetting cycles” was done by Beth Hoagland, Luke Mosley, Tess Russo, Jason Kirby, Cecilia Cullen, Matthew S. Fantle, Mark Raven and Joshua Fisher. Their study was featured by Science Digest website last January 2021.
Why is this study important in protecting the environment and in assuring health and safety to humans?
“The discharge of mine-derived hard rock and liquid tailings waste can alter water and sediment chemistry and release contaminants that pose risks to the functioning of aquatic ecosystems and human health (Nordstrom, 2011; Hudson-Edwards, 2016). Mining companies typically manage these risks by adding lime (Ca(OH)2, CaO) to tailings waste to increase alkalinity and pH and precipitate or co-precipitate metals out of solution. However, such approaches may not be as effective for metalloids (oxyanions), such as arsenic (As), whose response to liming is different than metals such as iron (Fe) (Jones et al., 1997; Smedley and Kinniburgh, 2002). Arsenic, a naturally-occurring metalloid associated with gold-bearing sulfide deposits (Corkhill and Vaughan, 2009; Nordstrom, 2011), is less strongly sorbed to minerals such as Fe-oxides at neutral-alkaline pH compared to metals such as zinc (Zn) and lead (Pb) (Jones et al., 1997). Thus, the efficacy of using lime to remove As from wastewaters is potentially limited as an As remediation strategy and depends on geochemical conditions in addition to pH (Moon et al., 2004; De Andrade et al., 2008; De Klerk et al., 2012)” 
How do we determine the treatment options for the removal of arsenic from mine wastes? For this, the geochemical conditions of the receiving environment must be considered.
“The background conditions of the environment receiving the wastes can influence the aqueous concentration, speciation (e.g. arsenite (As(III)) and arsenate (As(V)), and partitioning of As between water and sediment phases (Smedley and Kinnibrugh, 2002; Cheng et al., 2009). Such conditions include climate, the mineralogy of interacting sediments, and the chemistry of interacting waters (e.g. pH, Eh, and other chemical constituents present in solution).” 
With regards to the location of the study, its geographic and climatic features, the Porgera catchment is located in the headwaters of the Strickland Watershed in the Enga Province of the Papua New Guinea highlands (5◦27′ 47.83′′S, 143◦ 8′ 45.62′′E).
“Mean annual temperature in Porgera is 15.5 ◦C. The long-term mean annual precipitation is 3750 mm and the long-term daily mean precipitation is 10.4 mm, where precipitation events occur more than 300 days per year (Ross, 2012).” With the tropical rainfall that happens almost daily in Porgera, the mine-derived sediments then interact with dilute rainwaters.
The kind of rocks present in the highlands are underlain by igneous and sedimentary rocks, which host a suite of sulfide minerals such as pyrite (FeS2), sphalerite ((Zn,Fe)S), and galena (PbS).”
These sulfides have submicroscopic gold content, (pyrite and arsenical pyrite). These are extracted using acid-pressure oxidation and recovers using conventional cyanidation techniques (Fleming et al., 1986; King and Knight, 1992).
“After extraction, the mine separates the slurry from the gold-bearing solids and neutralizes associated wastewaters and waste sediments with lime (Ca(OH)2, CaO). The treated waste is discharged into the watershed and creates a braided, rocky channel known colloquially as the Red River.”
From the initial part of the study, they reported that “arsenic release related to gold mining activity can alter surface water and sediment chemistry. However, the toxicity of As in mine wastes, which is controlled by the speciation, concentration, and bioavailability of As, depends on the geochemical conditions of the impacted environment (e.g., pH, climate, mineralogy, etc).” 
“This study investigates the mechanisms of As partitioning into, or out of, streambed sediments downstream of the Porgera Gold Mine in Papua New Guinea.”
The use of lime as treatment for mine tailings and then discharged directly into the watershed makes the interaction prone to interaction with rain water. This reduces groundwater or acid rock drainage if it were to develop post mine-closure. 
One of the things to consider about the use of lime in the treatment of the mine tailings is that this practice increases the pH. This in effect triggers the precipitation of some trace metals that were derived from wastewaters. With an overall spike in pH, arsenic can now become more soluble.
For the study, the group conducted batch reactor experiments to bring out the effects of changing pH (ranging from 4 to 10) and wetting/drying cycles on arsenic interactions with lime-treated tailings. Another objective of the experiment is to understand the potential arsenic behavior following mine closure. 
“Across the pH range investigated, lime-treated waste sediments and streambed sediments located downstream of the open pit mine effectively scavenged As from the water column,” according to the study.
More specifically, tailings that were treated with lime buffered the pH. This reaction enhanced the interactions between dissolved arsenic and sediment surfaces via surface complexation reactions on amorphous iron oxides, “ as suggested by surface complexation modeling and batch reactor experimental results.” This “arsenic scavenging mechanism” further controlled and counteracted the increased solubility of arsenic at high pH.
Another aspect of the study was conducting a wetting/drying cycle experiments. From this, the group was able to infer that lime-treated tailings that are subjected to repeated wetting/drying cycles rapidly desorbed arsenic during the onset of rewetting, “but sorbed arsenic via an aluminum-bridging mechanism in subsequent wetting/drying cycles.” 
What useful information can we derive from these results?
In general, these results highlight the importance of continued lime treatment in order to lower the arsenic mobility in mine wastes following mine closure. This is applicable particularly for mine sites where wastes are released directly to the watersheds with no containment infrastructure to gather or filter out the outflow.
These results highlight the importance of continued lime treatment to reduce As mobility in mine wastes following mine closure, particularly for mine sites where wastes are released directly into watersheds with no containment infrastructure.
- Gold mine wastes treated with lime facilitated As removal via surface complexation.
- Lime-treatment enhances As sequestration by mine tailings from pH 4 to 10.
- Mineral saturation and Al-bridging influence [As] during wetting/drying cycles.
 Hoagland, Beth et. al. (January 2021). Science Direct - Applied Geochemistry. Volume 124. "Arsenic sequestration in gold mine wastes under changing pH and experimental rewetting cycles". Retrieved from - https://www.sciencedirect.com/science/article/pii/S088329272030281X
- Department of Geosciences, The Pennsylvania State University, University Park, PA, USA
- Acid Sulfate Soils Centre, The University of Adelaide, Adelaide, SA, Australia
- Earth and Environmental Systems Institute, The Pennsylvania State University, University Park, PA, USA
- CSIRO Land and Water, Contaminants and Biotechnology Program, Urrbrae, SA, Australia
- The Earth Institute, Columbia University, NY, NY, USA
About the map
Map of stream water and streambed sediment sampling sites in the Porgera Watershed. Shaded areas represent areas of concentrated gold mining activity mapped using Google Earth. Background colors correspond to surface elevation above mean sea level (m) determined from the SRTM 30m digital elevation model. The inset map highlights major watersheds of Papua New Guinea and the location of the Porgera catchment in the greater Strickland River watershed. The Anj-Kai label represents the confluence of the Anjolek and Kaiya Rivers. The Red-Up, Red-Mid, and Red-Pog represent sampling sites at the upstream and mid-stream locations in the treated wastes, and the confluence point of the treated waste stream and Pongema Rivers. Note that Yakatabari Creek, or the open pit runoff site, is a small tributary of Kakai River and the stream reach is not depicted on this map. The Yakatabari Creek sampling location is marked adjacent to Kakai River and upstream of the confluence point of these two reaches.
PNG Business News - February 23, 2021
St Barbara Transitions from Mining Oxide to Sulphide
St Barbara Ltd’s Simberi operations in New Ireland is set to transition from mining oxide ore to sulphide. The mine which has been producing gold since 2009 said that its social and environmental impact studies (SEIS) are presently being finished for submission to the Conservation and Environment Protection Authority (Cepa) and Mineral Resources Authority (MRA) in March.Sulphide mining is predicted to extend its mine life for at least another 10 years and produce more benefits for stakeholders.St Barabara managing director and chief executive Craig Jetson said, “We are at an important stage of operations at Simberi, as we continue to productively mine the oxide deposit and plan for a bright future via the Simberi sulphide project.”He added, “Iso will capably lead us through this transition as we support our Simberi community, contribute to New Ireland and deliver on our commitments to PNG.”Meanwhile, the firm said that since 2009, the mine has brought K84.3 million in royalties, paid an annual 0.5 per cent production levy and contributed over K97.4 million in contracts to landowner businesses.“In 2020, the company paid over K28 million in income tax,” according to St Barbara. “Other community benefits delivered since 2012, when St Barbara acquired the mine, amount to over K119 million. They include health and education infrastructure development, roads and bridges maintenance, cocoa farming, mariculture projects, education scholarships and employment and training.”
PNG Business News - February 23, 2021
Iso Ealedona Appointed General Manager for Simberi Mine
St Barbara Limited’s Simberi operations in the New Ireland province has a new general manager in the person of Iso Ealedona.Ealedona was previously the head of operations for the past seven months and is a mining engineer and pioneer of the PNG University of Technology mining degree program. With over 26 years of experience in the industry working in Australia for Rio Tinto Iron Ore and in PNG at Misima, Ok Tedi, Hidden Valley, Lihir and St Barbara’s Simberi Operations, his expertise includes operational leadership, technical services, maintenance, safety management and business transformation.“As a recognised employer of choice, we are proud to be the first public company (ASX listed) operating in PNG to entrust this important role to a capable Papua New Guinean with the right skills and experience to lead our 1200 strong workforce at Simberi,” he said. “We are at an important stage of operations at Simberi, as we continue to mine the oxide deposit and plan for a bright future via the Simberi sulphide project. Iso will capably lead us through this transition as we support our Simberi community, contribute to NIP and deliver on our commitments to PNG,” said Craig Jetson, St Barbara’s managing director and CEO.”He said, “It’s an honour to lead, on behalf of St Barbara, a mining operation in my home country. With the St Barbara executive, Simberi leadership team and the workforce behind me, I am determined to lead Simberi safely and successfully through this transition period of oxide to sulphide mining for the benefit of all stakeholders.”
PNG Business News - March 01, 2021
Landowners Support National Government on Wafi Golpu Project
The Wafi-Golpu landowners have finally voiced out their support to the National Government on the environmental permit given to mine developers. The five associations chairmen - Victor Geactuluc (Yanta Development Association), John Nema (Hengambu Landowner Association), Jack Raban (Babuaf Development Corporation) of the Special Mining Lease (SML) area including Joseph Tetang (Wampar Pipeline Association) and Gae Galang (Wagan Outfall Association) - said they want the project to proceed and are asking Morobe Governor Ginson Saonu to desist from any purported court proceedings against the Sate about the deep-sea tailings placement (DSTP).Saonu, however, said that Morobe’s position still stands. “I will do what is right, just and fair for everyone,” he said.According to an independent body monitoring and evaluating process for the last four years, the landowners shouldn’t rush into things. The leaders argued that this process may cost Morobe and the provincial government millions of kina and added that the mining forum is the best place to discuss this problem. Nema said that he has lost more than 20 of his community members to common natural calamities and lack of basic health services. “I am against the move by our governor to register another court proceeding against the National Government while my people are suffering and dying without seeing any real developments or benefiting from their land,” he said.Geactuluc said that they don’t support the intention of the governor to take this to court. “We urge the good governor to refrain from wasting his time with his consultants and advisers but instead commit his time and resource to mobilise the SML, Pipeline and Outfall landowners through their associations in preparation for the upcoming Wafi Project MoA,” he said.For his part, Tetang urged the governor to have a discussion on how he intends to recognise the Huon Gulf coastal communities benefit-sharing instead of fighting a losing arrangement to prevent DSTP. “That is why the developer has chosen DSTP because it is much safer and could not harm the marine resources or the coastal communities based on the research and studies conducted,” he said.
PNG Business News - July 22, 2021
Oil Search Considering Merging with Santos
Santos, an Australian oil firm, announced its plan to combine with Oil Search Limited. Santos proposed a non-binding indicative merger last month with the goal of making the two companies the regional energy champions. The proposed merged entity has a market capitalization of A$22 billion (K56 billion), putting it among the top 20 ASX-listed companies and the top 20 global oil and gas companies. This means, among other things, that the merger will have a diverse portfolio of high-quality, long-life assets spanning Australia and Papua New Guinea, a solid balance sheet with ample cash to support expansion choices, and an investment-grade credit rating. The merger plan, if approved, would be conducted through a Scheme of Arrangement in which Oil Search shareholders would receive 0.589 new Santos shares for each Oil Search share held, according to Santos in a market disclosure to the Australian Stock Exchange. Following the scheme's acceptance, Oil Search shareholders would control 37% of the combined company, while Santos shareholders would own 63%. Based on Santos' closing price on June 24, 2021, the ownership ratio suggested a transaction price of A$4.25 (10.92) per Oil Search share. This was a 12.3% premium to the Oil Search closing price of A$3.78 (K9.72) on June 24, 2021, and a 9.8% premium to the Mubadala block trade selling price of A$3865. (K9.92). Kevin Gallagher, managing director and chief executive officer of Santos, said the merger will bring more alignment to PNG, allowing for the development of important projects such as Papua LNG, as well as the creation of new employment and support for the local economy. Santos, according to Gallagher, has proposed a true merger in which ownership of the combined firm is based on proportionate contribution and value. “The strategic rationale for a merger is clear and offers superior value to Oil Search shareholders rather than continuing on a standalone basis. “Santos continues to believe that the Merger Proposal represents an extremely attractive opportunity to deliver compelling value accretion to both Santos and Oil Search shareholders.” Oil Search stated in its ASX market update that it is open to receiving and engaging with any proposal that is in the best interests of its shareholders. While the company's board of directors agrees with Santos that combining the two firms makes strategic sense, the conditions must be fair to the company's shareholders, which the terms proposed by Santos are not. Despite Santos shareholders holding 70% more shares than Oil Search shareholders, Oil Search maintains that the proposed conditions provide just a 6.8% premium based on Friday's closing share prices for Oil Search and Santos. According to the firm, no such proposal has been made at this time. Reference: Post-Courier (21 July 2021). "Oil Search Open To Merger with Santos".
PNG Business News - July 21, 2021
Study Says Sweet Potato Growers Have Received Significant Insights into Customers Buying Habits
In Papua New Guinea (PNG), sweet potato (kaukau) growers have received significant insight into customer buying habits, which is assisting them in identifying new market possibilities. The recent market analysis, which was supported by the Papua New Guinea-Australia Partnership and conducted by the Australian Centre for International Agricultural Research, revealed that an increasing number of consumers in Port Moresby prefer to buy fresh produce from supermarkets, citing convenience and safety as reasons. While this trend may result in fewer consumers at conventional farmer markets, PNG and Australian experts believe it may open up new marketplaces for rural people. “Farmers are looking for stable markets where they can receive more consistent prices for better-quality produce,” said Professor Philip Brown from Central Queensland University (CQU), who is leading the research project. “The research shows that consumer behaviour is likely to support an expansion in the supermarket sector in large urban centres and this is positive news for the farmers. This could allow commercial focused farmers to secure more stable market access.” The study of 353 customers was conducted as part of ACIAR-funded sweet potato research sponsored by CQU and the PNG National Agriculture Research Institute (NARI), which aims to improve sweet potato value chains by increasing the quality of harvested roots. Sweet potato quality and production are improving, resulting in increasing supplies to retailers eager to provide better fresh produce. “The project, with support from the Fresh Produce Development Agency and NARI, is helping farmers to build their business skills and connect with emerging supermarket opportunities,” said Professor Brown. Kirt Hainzer, a CQU researcher who collaborated on the survey alongside NARI researchers, said it was the first study to look at customer behaviour and see what role stores may play in the development of PNG's commercial sweet potato sector. “The research sought to better understand and compare how consumers buy staples from open markets and supermarkets and to explore the preferences for purchasing staple foods as supermarkets increase the availability of convenience staples like rice,” said Hainzer. “Although expanding formal sales represents a huge step forward in developing a commercial sweet potato industry, continued research on consumer preferences and the market for fresh produce will help better understand trends in staple food purchasing and what market opportunities exist for growers.” With over a hundred kinds of sweet potato in the nation, NARI economist Raywin Ovah said the study sought to find out which of these customers preferred. “Not all the varieties are preferred from a consumer point of view. There are only a few that consumers want to be based on the taste or health properties and that is what we want to also find out. Farmers can be provided with that information, so they produce those varieties that the market wants.” One of five initiatives under the Transformative Agriculture and Enterprise Development Program is a project to increase commercial sweet potato production and commercialization in the PNG highlands. The ACIAR program, which is funded by Australia in collaboration with the government of Papua New Guinea, aims to improve the livelihoods of rural men and women through private sector-led development, increased agricultural productivity and quality, and the development of individual and institutional capacity. Reference: Loop (20 July 2021). “Study looks into sweet potato industry”.
PNG Business News - July 21, 2021
Garry: MRA Evaluating K50 Billion Worth of Investments
According to managing director Jerry Garry, the Mineral Resources Authority is evaluating more than K50 billion in investments in the country. Wafi-Golpu, Frieda River, and Woodlark are among them. “We are also looking at the Central Lime and Cement,” he said. “If that project comes on-stream, it will be one of the first industrial mines ever built in the country.” Garry was speaking at a Port Moresby consultation session on the Mine and Works (Safety and Health) Bill 2021. PNG, he added, was home to some of the world's largest mines. “We have grown from strength to strength,” he said. “If you compare the Bank of PNG statistics, the mining sector alone, in terms of production, has exported over K17 billion in 2020 and 2019. “So it’s a huge industry that we are trying to regulate and manage.” Garry expressed gratitude to the industry for making safety a primary priority. “They have been taking health and safety at the workplaces very seriously,” he said. “We must not only consider (the workers) and the environment but also people living around the (areas) we operate in. “And if we are using any hazards, we must also take responsibility.” The newest mining methods in Wafi-Golpu, known as block cave mining, are one of the new things to expect, according to Garry. “New mining hazards will come with this new mining method,” he said. Reference: The National (20 July 2021). “Authority assessing investments worth K50bil”.