{"id":8218,"date":"2026-10-13T23:42:09","date_gmt":"2026-10-13T15:42:09","guid":{"rendered":"https:\/\/junglenical.com\/?p=8218"},"modified":"2026-10-13T23:42:13","modified_gmt":"2026-10-13T15:42:13","slug":"method-for-recovering-gold-from-activated-carbon","status":"publish","type":"post","link":"https:\/\/junglenical.com\/ja\/blog\/method-for-recovering-gold-from-activated-carbon\/","title":{"rendered":"Method for Recovering Gold from Activated Carbon"},"content":{"rendered":"

Gold rarely occurs in a form that can be mined and sold directly. Most of it sits in low-grade ore that must be dissolved, concentrated, and re-solidified before it has any commercial value. Since the early 1980s, the industry has relied on activated carbon to perform that concentration step, replacing zinc-dust precipitation at most operations. Today, the method a plant chooses and the quality of the carbon it buys determine whether dissolved gold leaves the circuit as saleable bullion or disappears into tailings as unrecovered value, which makes carbon-based recovery one of the most consequential decisions in modern gold processing.<\/p>\n\n\n\n

Activated carbon recovers gold by adsorbing gold-cyanide complexes from leach solutions inside carbon-in-pulp (CIP), carbon-in-leach (CIL), and carbon-in-column (CIC) circuits. Granular activated carbon for gold recovery<\/a> draws dissolved Au(CN)\u2082\u207b ions into its micropore network, concentrating gold from less than one part per million in solution to 4,000\u20138,000 grams per tonne of carbon. Loaded carbon is then stripped through Zadra or AARL elution, the concentrated eluate passes through electrowinning or zinc precipitation, and the recovered sludge is smelted into dor\u00e9 bullion. Spent carbon is thermally regenerated and returned to service, often for 20 or more adsorption cycles before replacement.<\/strong><\/p>\n\n\n\n

The sections below walk through each stage in detail: how adsorption works, how the three methods differ, how gold is stripped from loaded carbon, which carbon specifications matter most, and how disciplined carbon management protects both recovery and operating cost.<\/p>\n\n\n\n

What Is Activated Carbon for Gold Recovery and How Does It Work?<\/h2>\n\n\n\n
\"Close-up<\/figure>\n\n\n\n

Activated carbon recovers gold through physical adsorption: porous carbon granules attract and hold dissolved gold-cyanide complexes inside an internal pore network that can exceed 1,000 square meters per gram.<\/strong> Because the gold is held on the carbon surface rather than consumed in a chemical reaction, adsorption is fast, selective, and fully reversible during elution, which is exactly what a recirculating recovery circuit needs.<\/p>\n\n\n\n

The process begins with cyanidation. Gold has no natural affinity for water, so plants dissolve it using oxygen and \u30b7\u30a2\u30f3\u5316\u30ca\u30c8\u30ea\u30a6\u30e0<\/a>, which form the stable complex ion Au(CN)\u2082\u207b. Free cyanide in solution typically runs between 100 and 500 parts per million depending on ore demand, and dissolved oxygen keeps the dissolution reaction moving. Once the complex forms, the carbon side of the circuit takes over.<\/p>\n\n\n\n

Adsorption itself is driven by pore geometry and surface chemistry. The Au(CN)\u2082\u207b ion is a linear complex roughly 0.6\u20130.8 nanometers long, and gold-grade carbons develop pore networks in which most of the pore volume sits in micropores below 2 nanometers, a near-ideal fit. Larger contaminant molecules are excluded at the pore mouth, which gives the carbon its selectivity, while mesopores act as transport channels feeding the micropore network. Adsorption kinetics depend on solution temperature, pH, free cyanide concentration, and carbon activity.<\/p>\n\n\n\n

Separation is the other half of the elegance. Carbon granules for slurry circuits are typically 6\u00d712 mesh, about 1.7\u20133.35 mm, hundreds of times larger than the ground ore particles they move through, so inter-stage screens retain the carbon while pulp passes through. A tonne of well-loaded carbon at the end of a circuit can hold 4,000\u20138,000 grams of gold, a concentration factor of several million versus the head solution.<\/p>\n\n\n\n

From Cyanide Leaching to Loaded Carbon<\/h3>\n\n\n\n

The full carbon-based recovery loop runs through eight steps:<\/p>\n\n\n\n

    \n
  1. Crushing and grinding<\/strong> reduce the ore to particles fine enough to expose gold surfaces to solution.<\/li>\n\n\n\n
  2. Leaching<\/strong> dissolves the gold as Au(CN)\u2082\u207b under alkaline conditions, usually at pH 10.5\u201311.<\/li>\n\n\n\n
  3. Adsorption<\/strong> contacts the gold-bearing slurry or solution with granular carbon in tanks or columns, almost always counter-current.<\/li>\n\n\n\n
  4. Screening<\/strong> retains carbon at each stage while advancing progressively loaded carbon against the flow.<\/li>\n\n\n\n
  5. Elution<\/strong> strips the gold from loaded carbon into a small volume of concentrated pregnant eluate.<\/li>\n\n\n\n
  6. \u96fb\u89e3\u7cbe\u932c<\/strong>, or zinc precipitation in older plants, deposits the gold from the eluate onto cathodes.<\/li>\n\n\n\n
  7. Smelting<\/strong> converts the cathode sludge into dor\u00e9 bars.<\/li>\n\n\n\n
  8. \u518d\u751f<\/strong> thermally reactivates the stripped carbon, which then returns to the adsorption circuit.<\/li>\n<\/ol>\n\n\n\n

    CIP vs CIL vs CIC: Three Methods for Recovering Gold with Activated Carbon<\/h2>\n\n\n\n

    All three methods rely on the same adsorption chemistry; they differ in where the carbon meets the gold-bearing stream.<\/strong> CIP adsorbs dissolved gold after leaching is largely complete, CIL adsorbs while leaching is still running, and CIC treats clarified solution in fixed columns. Ore metallurgy, plant throughput, and leach kinetics decide which arrangement wins.<\/p>\n\n\n\n

    Carbon-in-Pulp (CIP)<\/h3>\n\n\n\n

    In CIP, leached pulp flows through a train of four to six agitated adsorption tanks. Carbon is retained in each tank by inter-stage screens and advanced counter-current to the pulp, so the freshest carbon meets the lowest-grade pulp in the final tank, where it still pulls trace gold from solution that is about to become tailings. Carbon concentration typically runs 15\u201325 grams per liter per tank. Because leaching and adsorption are physically separated, operators can tune each stage independently, which makes CIP attractive for ores with predictable leach behavior.<\/p>\n\n\n\n

    Carbon-in-Leach (CIL)<\/h3>\n\n\n\n

    CIL runs leaching and adsorption in the same tank train, with carbon present while cyanide is still dissolving gold. This matters for two ore types. Preg-robbing ores contain natural organic carbon that re-adsorbs dissolved gold before the plant can capture it, and adding activated carbon early gives the dissolved gold a competitive surface while shifting the equilibrium back toward recovery. Slow-leaching ores also benefit, because continuous adsorption keeps the solution gold tenor low throughout the leach. The trade-offs are a larger carbon inventory, more attrition exposure, and less independence between the two processes.<\/p>\n\n\n\n

    Carbon-in-Column (CIC)<\/h3>\n\n\n\n

    CIC serves heap leach operations and other clear-solution duties. Pregnant solution draining from a heap is clarified and passed through columns packed with \u7c92\u72b6\u6d3b\u6027\u70ad<\/a>, often arranged in lead, lag, and polish sequences. Because no slurry is present, the carbon suffers little attrition, inter-stage screens are unnecessary, and finer mesh sizes can be used for faster kinetics. CIC columns are also widely used to polish barren solution and treat mine water, recovering residual gold while tightening environmental compliance.<\/p>\n\n\n\n

    \u56e0\u5b50<\/td>CIP<\/td>CIL<\/td>CIC<\/td><\/tr>
    Adsorption timing<\/td>After leaching<\/td>During leaching<\/td>After heap leaching<\/td><\/tr>
    Feed<\/td>Ground slurry<\/td>Ground slurry<\/td>Clarified solution<\/td><\/tr>
    Carbon state<\/td>15\u201325 g\/L suspension per tank<\/td>15\u201325 g\/L suspension per tank<\/td>Fixed beds in columns<\/td><\/tr>
    \u6700\u9069\u306a\u30b5\u30a4\u30ba<\/td>Predictable leach kinetics; independent stage control<\/td>Preg-robbing or slow-leaching ores<\/td>Low-grade ores and heap leach pads<\/td><\/tr>
    Attrition exposure<\/td>\u9ad8\u3044<\/td>\u9ad8\u3044<\/td>\u4f4e<\/td><\/tr>
    Screen requirement<\/td>Inter-stage screens essential<\/td>Inter-stage screens essential<\/td>Not required<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    How Is Gold Recovered from Loaded Activated Carbon? (Elution to Bullion)<\/h2>\n\n\n\n
    \"A<\/figure>\n\n\n\n

    Gold is stripped from loaded carbon by elution: a hot, strongly alkaline solution reverses the adsorption equilibrium and washes the gold-cyanide complex off the carbon into a small volume of concentrated pregnant eluate, from which gold is won by electrowinning or zinc precipitation and smelted into bullion.<\/strong> A single strip cycle recovers the majority of the 4,000\u20138,000 grams of gold per tonne carried by loaded carbon.<\/p>\n\n\n\n

    Elution works because adsorption is exothermic and reversible. Raising the eluant to 90\u2013130\u00b0C while maintaining caustic and cyanide chemistry destabilizes the bond between the gold-cyanide complex and the carbon surface. The eluant is blended from the same gold recovery chemicals<\/a> used across the cyanidation plant, chiefly caustic soda and cyanide salts, and because it circulates through a compact column rather than the whole adsorption train, the gold reports to a working volume thousands of times smaller than the leach circuit. Two industrial elution methods dominate worldwide: Zadra and AARL.<\/p>\n\n\n\n

    Zadra Elution Process<\/h3>\n\n\n\n

    The Zadra process, developed at the U.S. Bureau of Mines, operates at atmospheric pressure. A hot solution of 1\u20132% \u6c34\u9178\u5316\u30ca\u30c8\u30ea\u30a6\u30e0<\/a> with 0.1\u20130.5% sodium cyanide is recirculated through the strip column at 90\u201395\u00b0C, passing continuously through an electrowinning cell so that elution and gold deposition happen simultaneously. Cycle times range from roughly 24 to 72 hours depending on column design and carbon loading. The flowsheet is simple and capital-light, which keeps Zadra popular at smaller operations, although its long cycles and dilute eluate, typically 50\u2013200 mg\/L of gold, raise energy and electrowinning costs at scale. Peer-reviewed parameter sets for both Zadra and AARL are documented in the Journal of Chemical Technology and Metallurgy<\/a>, a practical reference for engineers comparing the two routes.<\/p>\n\n\n\n

    AARL Elution Process<\/h3>\n\n\n\n

    The AARL process, named after the Anglo American Research Laboratories in South Africa, trades a pressure vessel for speed. Loaded carbon is first acid-washed with roughly 3% hydrochloric acid to strip calcium carbonate scale, rinsed, pre-soaked in a caustic-cyanide solution, and then eluted with hot softened or deionized water at 110\u2013130\u00b0C under 2\u20133 bar of pressure. Strips complete in roughly 8\u201316 hours and produce a more concentrated eluate, 200 to 1,000 mg\/L of gold, that electrowins efficiently. The method decouples elution from electrowinning, but it demands pressure-rated equipment, consistent water quality, and tighter process control, which suits larger plants better than small ones.<\/p>\n\n\n\n

    \u30d1\u30e9\u30e1\u30fc\u30bf<\/td>Zadra<\/td>AARL<\/td><\/tr>
    Operating pressure<\/td>Atmospheric<\/td>2\u20133 bar<\/td><\/tr>
    \u6e29\u5ea6<\/td>90\u201395\u00b0C<\/td>110\u2013130\u00b0C<\/td><\/tr>
    Typical cycle time<\/td>24\u201372 hours<\/td>8\u201316 hours<\/td><\/tr>
    Eluant<\/td>Hot caustic cyanide, recirculated<\/td>Acid wash, caustic soak, hot softened water<\/td><\/tr>
    Eluate gold tenor<\/td>50\u2013200 mg\/L<\/td>200\u20131,000 mg\/L<\/td><\/tr>
    Capital and complexity<\/td>Lower, simpler flowsheet<\/td>Higher, pressure vessel and water treatment<\/td><\/tr>
    \u6700\u9069\u306a\u30b5\u30a4\u30ba<\/td>Operations below roughly 500 tpd<\/td>Larger operations with steady throughput<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    Electrowinning, Zinc Precipitation and Smelting<\/h3>\n\n\n\n

    Pregnant eluate is pumped through electrowinning cells, where an applied current deposits gold onto steel wool or mesh cathodes. The loaded cathodes are periodically washed, and the resulting sludge is filtered, dried, fluxed, and smelted into dor\u00e9 bars that typically assay 80\u201395% gold before refining. Where solutions are exceptionally clear and high-grade, zinc-dust precipitation in the Merrill-Crowe configuration remains a workable alternative, but electrowinning dominates modern carbon plants because it handles dilute eluates and integrates directly with Zadra circulation. The stripped carbon, now called lean carbon, still carries residual foulants and heads to regeneration.<\/p>\n\n\n\n

    Why Coconut Shell Activated Carbon Is the Industry Standard<\/h2>\n\n\n\n

    Coconut shell activated carbon dominates gold recovery because it pairs the highest mechanical hardness of any common carbon with a micropore structure sized for the gold-cyanide complex, cutting carbon losses and gold-in-fines while loading gold faster than the alternatives.<\/strong> More than 95% of the activated carbon used in gold and silver recovery worldwide is steam-activated coconut shell carbon.<\/p>\n\n\n\n

    The agitation in CIP and CIL service is relentless: carbon is pumped between tanks, screened, acid-washed, stripped at high temperature, and kiln-regenerated, cycle after cycle. Every particle that abrades into fines can pass the inter-stage screens and carry its adsorbed gold straight into the tailings. \u30b3\u30b3\u30ca\u30c3\u30c4\u6bbb\u7531\u6765\u306e\u6d3b\u6027\u70ad<\/a> answers this with ball-pan hardness of 95\u201399%, versus roughly 85\u201392% for coal-based grades, and its dense micropore network matches the small Au(CN)\u2082\u207b ion. Low ash content keeps the pores open, and the uniform raw material delivers batch-to-batch consistency that mine buyers can write into specifications.<\/p>\n\n\n\n

    Coconut Shell vs Coal-Based and Wood-Based Carbon<\/h3>\n\n\n\n

    \u77f3\u70ad\u7531\u6765\u306e\u6d3b\u6027\u70ad<\/a> costs less per tonne and performs well in water treatment and vapor-phase duties, but in agitated gold circuits its lower hardness and broader pore distribution usually cost more than they save:<\/p>\n\n\n\n

    \u30d7\u30ed\u30d1\u30c6\u30a3<\/td>\u30b3\u30b3\u30ca\u30c3\u30c4\u306e\u6bbb<\/td>\u77f3\u70ad\u3092\u539f\u6599\u3068\u3059\u308b<\/td>\u6728\u6750\u7cfb<\/td><\/tr>
    \u30dc\u30fc\u30eb\u30d1\u30f3\u786c\u5ea6<\/td>95\u201399%<\/td>85\u201392%<\/td>Below 85%<\/td><\/tr>
    Micropore volume<\/td>\u9ad8\u3044<\/td>\u4e2d\u7a0b\u5ea6<\/td>\u4f4e\uff5e\u4e2d\u7a0b\u5ea6<\/td><\/tr>
    Gold adsorption kinetics<\/td>Fast<\/td>\u4e2d\u7a0b\u5ea6<\/td>Slow<\/td><\/tr>
    Attrition loss per cycle<\/td>0.5\u20131.5%<\/td>2\u20134%<\/td>\u9ad8\u3044<\/td><\/tr>
    Typical reuse cycles<\/td>18\u201322+<\/td>8\u201312<\/td>\u6570\u91cf\u9650\u5b9a<\/td><\/tr>
    Total cost per ounce recovered<\/td>Usually lowest<\/td>Higher through fines losses<\/td>Unsuitable for slurry circuits<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    Wood-based carbons, though inexpensive and highly porous, rarely survive slurry service and are confined to clarification and polishing duties where mechanical stress is minimal.<\/p>\n\n\n\n

    Key Specifications for Gold Recovery Carbon<\/h3>\n\n\n\n

    Procurement should be specification-driven rather than price-driven. The parameters below decide in-plant performance and belong in any purchase contract:<\/p>\n\n\n\n

    \u30d1\u30e9\u30e1\u30fc\u30bf<\/td>Typical specification<\/td>\u305d\u306e\u91cd\u8981\u6027<\/td><\/tr>
    \u30e8\u30a6\u7d20\u4fa1<\/td>\u22651,050 mg\/g, premium \u22651,100<\/td>Proxy for micropore volume; correlates with gold loading capacity<\/td><\/tr>
    \u30dc\u30fc\u30eb\u30d1\u30f3\u786c\u5ea6<\/td>\u226595%, premium \u226598%<\/td>Directly controls attrition, carbon loss, and gold-in-fines<\/td><\/tr>
    \u7c92\u5b50\u5f84<\/td>6\u00d712 or 6\u00d716 mesh<\/td>Balances adsorption kinetics against screen retention<\/td><\/tr>
    \u7070\u5206<\/td>\u22643%<\/td>Ash blocks micropores and depresses capacity<\/td><\/tr>
    \u6c34\u5206<\/td>\u22645%<\/td>Protects dosing accuracy and shipping weight<\/td><\/tr>
    Gold adsorption rate (k-value)<\/td>\u22653.0 in a 4-hour test<\/td>Best single predictor of in-circuit kinetics<\/td><\/tr>
    \u898b\u304b\u3051\u306e\u5bc6\u5ea6<\/td>0.48\u20130.54 g\/mL<\/td>Affects settling, transfer, and screening behavior<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    Iodine number is measured with the ASTM D4607 standard test method<\/a>, and hardness by the ASTM D3802 ball-pan procedure; both should be paired with batch certificates of analysis. Because these indices interact, a carbon that excels on one metric but fails on hardness will still lose money in an agitated circuit.<\/p>\n\n\n\n

    How to Optimize Carbon Management and Minimize Gold Losses<\/h2>\n\n\n\n

    Most avoidable gold losses in carbon circuits trace back to carbon fines, screen failures, and fouled carbon, and disciplined carbon management can claw back several percentage points of overall recovery without new equipment.<\/strong> The practices below are standard at well-run CIP and CIL plants:<\/p>\n\n\n\n