Green Solutions for Gold Mining: Sodium Cyanide Substitutes in Indonesia

Indonesia is the largest country in ASEAN, with a land area of 1.919 million square kilometers and a marine area of 3.16 million square kilometers (excluding the exclusive economic zone). The country is rich in mineral resources. Major metallic minerals include bauxite, nickel, iron sand, copper, tin, gold, and silver; non-metallic minerals mainly consist of coal, limestone, and granite. There are also certain reserves of zinc, mercury, manganese, lead, kaolin, andesite, quartz sand, feldspar, dolomite, bentonite, zeolite, phosphate, and gypsum. However, due to outdated geological exploration technology, weak statistical work, and poor resource development and utilization capabilities, the government has an incomplete understanding of its own resource reserves. For a long time, mineral resources have primarily been developed and utilized by foreign companies. According to statistics from Indonesia's Ministry of Energy and Mineral Resources, the gold mineral resource reserves and distribution are as follows: gold reserves are approximately 1.91 million tons, with proven reserves of 3.200 tons, mainly distributed in Sumatra, Sulawesi, Kalimantan, and Papua. In 2023. the production was about 132 tons, with approximately 890 kilograms of gold bars exported. Gold mining has attracted many Chinese businessmen and investors. In Indonesia, gold mines are generally classified into alluvial gold mines and oxidized ores. The heap leaching process used for oxidized ores is widely adopted due to its low investment and quick returns. However, heap leaching construction is constrained by procurement, information sources, and construction technology, leading most mine owners to initially use Sodium cyanide.

Sodium cyanide poses several issues in Indonesia. First, the procurement cost is high, with a market price of about 50.000 to 60.000 RMB per ton. Second, sodium cyanide is highly toxic; inhalation, ingestion, or dermal absorption can lead to acute poisoning. Third, sodium cyanide is subject to strict regulation by the Indonesian government, with stringent approvals and management for sales, storage, and transportation. These issues are well understood by our Chinese investors, but there has always been a lack of effective alternative solutions.

As early as 2016. several environmentally friendly gold extraction agents were developed in China and have been widely used. Shaanxi United Chemical is a company focused on the production and research of hydrogen cyanide derivatives and environmentally friendly gold extraction agents. The actual performance of Shaanxi United's environmentally friendly gold extraction agents can replace sodium cyanide and has been sold and used in more than ten countries worldwide, receiving widespread praise from customers.

1. The characteristics of Shaanxi United's environmentally friendly gold extraction agents are as follows:

2. they are environmentally friendly and green products (tested by authoritative departments, the products are classified as ordinary goods);

3. they have a high recovery rate (suitable for heap leaching, pool leaching, stirring leaching, etc.);

4. they have good stability (with effective stabilizers added to reduce interference from harmful substances such as S and As);

5. they have a wide range of applications (used in gold oxidized ores, primary ores, sulfuric slag, gold concentrates, anode mud, etc.);

6. they are easy to use (pH value of 10-12. dosage and method can be completely aligned with cyanide processes);

7. they are reasonably priced, significantly reducing investment costs compared to sodium cyanide.

Usage Instructions

1. Application Scope：

1. Applicable Ore Types: Gold and silver oxide ores, native ores, high-sulfur and high-arsenic gold ores, cyanide tailings, gold concentrates, sulfuric acid residues, anode mud, etc.

2. Applicable Mineral Processing Techniques: Heap leaching, pond leaching, carbon-in-pulp (stirred leaching), etc.

2. Product Form: Solid powder or granular form

3. Dissolution Method: Fully dissolve in water at room temperature before use (generally, dissolution can be accelerated in flowing water or by thorough stirring; during heap leaching, a dosing pool can be built at the edge of the poor solution pool to allow the return water after activated carbon treatment to wash the gold extraction agent into the poor solution pool).

4. pH Adjustment: Generally, lime or sodium hydroxide is used to adjust and maintain the pH value between 10-12; when the return water pH value decreases, alkalinity should be adjusted in a timely manner; if the pH value remains too high (greater than 12) for an extended period, it may lead to the formation of alkaline scale affecting activated carbon adsorption or cause liquid passivation affecting leaching efficiency.

5. Dosage Calculation：

1. The dosage can be referenced from the usage amount of sodium cyanide, and it is recommended to conduct mineral processing tests and refer to optimal conditions (commonly about 1-2 g/t for gold oxide ores, with the concentration of the gold extraction agent generally maintained at 0.3-0.8‰, adjusted according to different ore grades and harmful components).

2. Calculation Method for Dosage: The supplementary dosage of the gold extraction agent = (optimal concentration value - current measured concentration value) × volume of water in the dosing pool; for example, if the optimal concentration value of the gold extraction agent is 1.5‰ (based on water volume), and the return water concentration is 0.6‰, with 500 cubic meters of water in the poor solution pool, then the supplementary dosage would be: (1.5 - 0.6) × 500 = 450 kg.

6. Product Usage Process: (Consistent with the use of sodium cyanide in heap leaching and carbon leaching processes)

1. Heap Leaching and Pond Leaching Process: Crush the raw ore, pile/pool it, leach, adsorb with activated carbon (zinc powder replacement), electrowinning, and smelting.

2. Carbon-in-Pulp Process (Stirred Leaching): Crush the raw ore, grind it, carbon leach, electrowinning, and smelting.

Successful Case of Environmentally Friendly Gold Extraction Reagent

The Lingbao Wenyu Gold Mine in Henan has conducted laboratory and industry tests using a new low-toxicity gold extraction reagent technology in its full lime cyanidation project. The tests achieved ideal processing indicators. When the grinding fineness was -0.074mm with a content greater than 90%, the pulp concentration was 40%, the lime dosage was 3kg/t, the alkaline pretreatment time was 2 hours, the dosage of the environmentally friendly gold leaching agent was 600g/t, and the leaching time was 24 hours, the gold leaching rate reached 95.60%. The test results demonstrate that this reagent can replace sodium cyanide in the gold extraction process. Currently, the reagent has been put into use. Compared to cyanide leaching, the leaching rate increased by 1.4%, the dosage of the reagent was reduced by 200g/t, and the leaching time was shortened by more than 12 hours. Additionally, a leaching toxicity analysis of the tailings from the environmentally friendly gold leaching agent showed that the leaching toxicity values of cyanide, copper, lead, zinc, and arsenic in the tailings were all within standard limits, allowing for direct discharge without the need for detoxification treatment.

Regarding the use of environmentally friendly gold selection agents, it is necessary to have a professional technician conduct tests in the early stages of mining. This is because different mining areas and different types of ore will yield varying results with the selection agents. The appropriate dosage and whether to add other chemical materials must be determined based on preliminary tests. During this period, Shaanxi United Chemical will provide all the necessary services to assist you in completing the tests.

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