Coconut Shell Activated Carbon

1.Q: Why is coconut shell activated carbon commonly preferred over coal-based or wood-based carbon for gold recovery?

A: The key reason is the match between the microporous structure and the gold cyanide complex. Gold exists mainly as [Au(CN)₂]⁻, with an ionic size of about 1 nm, which fits the micropore range dominant in coconut shell activated carbon (<2 nm micropores can account for more than 80% of total porosity). Coal-based carbon has a higher proportion of mesopores and macropores, and its micropore volume is typically only 60%–70% of that of coconut shell carbon. Wood-based carbon has uneven micropore distribution and thinner pore walls, making pores prone to blockage or collapse during long-term slurry immersion. Coconut shell carbon can reach a saturated adsorption capacity of 800–1200 g/t for [Au(CN)₂]⁻, compared with about 500–800 g/t for coal-based carbon and 400–600 g/t for wood-based carbon. Coconut shell carbon also has higher hardness, with attrition in CIP/CIL tanks typically only 1%–2% per cycle and a cyclic service life of 8–10 cycles, versus 5–7 cycles for coal-based carbon.

2.Q: What iodine value should premium coconut shell activated carbon for gold recovery have? Is higher always better?

A: Higher is not necessarily better. Iodine value reflects micropore development and adsorption capacity potential, but gold recovery also requires balanced desorption/elution feasibility. The preferred range for most mines is 1000–1100 mg/g. For conventional oxide ore CIL circuits, 1050 ± 50 mg/g is often regarded as the most cost-effective window balancing adsorption capacity and elution efficiency. Above 1150 mg/g, the micropores may bind the gold cyanide complex too strongly, leading to difficult elution and incomplete gold stripping; gold loading may actually decline over repeated cycles. Below 950 mg/g, loading capacity is insufficient, requiring more frequent carbon addition and increasing carbon consumption. Selection should target the process-matched window rather than simply the highest number on a certificate.

3.Q: What is the adsorption mechanism of gold cyanide complex on activated carbon, and what does it mean for selection?

A: Adsorption of [Au(CN)₂]⁻ on activated carbon is not a single mechanism; it involves micropore filling, weak π-electron donor interactions and ion-pair adsorption. After adsorption, the gold cyanide complex largely retains its chemical form, which supports subsequent elution and recovery. For selection, this means micropore volume and pore-size distribution are more meaningful than total specific surface area alone: the more micropores with apertures matching [Au(CN)₂]⁻, the denser the effective adsorption sites. At the same time, excessive surface oxygen-containing functional groups may enhance competitive adsorption of impurity ions such as copper and iron, so ash content and metal leaching indicators should also be controlled.