Q: What is iodine number and how does it relate to adsorption capacity?

Iodine number (mg I₂ adsorbed per g AC) is the standard indicator of micropore volume and small-molecule adsorption capacity. Higher iodine number = more micropores = better removal of taste & odor, THMs, and small organics. Typical values: 800–900 mg/g (industrial), 900–1000 mg/g (water treatment), >1000 mg/g (premium drinking water / gold recovery). The iodine number test (ASTM D4607) measures how much iodine (a small molecule, MW 254 g/mol, effective diameter ~0.6 nm) is adsorbed from standard iodine solution by 0.1 g AC in a set contact time. It specifically measures micropore volume (pores accessible to I₂). For drinking water taste & odor (geosmin effective diameter ~0.7 nm; 2-MIB ~0.6 nm), iodine number correlates well with removal capacity. For larger contaminants like color (humic acids, MW > 500 g/mol, effective diameter >1.5 nm) or dyes, methylene blue number (MB number) is more relevant — it measures mesopore adsorption. An AC with high iodine number but low MB number has excellent micropores but poor mesopores (typical of coconut shell) and will remove taste & odor well but remove large-molecule color poorly. For gold cyanide adsorption in CIP/CIL circuits, the gold loading capacity (kg Au / ton AC) is the operational parameter that matters — coconut shell ACs with iodine >1100 mg/g achieve 7–12 kg Au/ton vs coal-based ACs achieving 4–8 kg Au/ton. Always request the specific contaminant-relevant specification (not just iodine number) when ordering for a specific application.

Q: What documents are available — COA, test certificates?

Standard COA includes: iodine number (ASTM D4607), methylene blue number, moisture content, ash content, hardness number (ASTM D3802), pH, and particle size distribution. Drinking water grades: NSF/ANSI Standard 61 certification per batch. Gold recovery grades: gold adsorption capacity test (Mintek or equivalent). Vapor phase grades: CTC activity (ASTM D3467), apparent density. Activated carbon COA parameters and their significance: Iodine number (ASTM D4607) — primary indicator of micropore volume; test measures mg I₂ adsorbed by 1g AC from 0.1N I₂ solution; minimum specs: 900 mg/g for water treatment, 1000 mg/g for drinking water. Methylene blue (MB) number — indicates mesopore volume; minimum 150 mg/g for general water treatment, >200 mg/g for color removal. Moisture content — should be 15%) indicates coal-based with high mineral content, which affects adsorption selectivity. Hardness number (ASTM D3802 ball-pan hardness) — measures resistance to abrasion in standard tumbling test; gold recovery carbon requires ≥97% hardness; drinking water GAC requires ≥90%; industrial GAC ≥85%. pH (slurry) — should be 7–10 for most applications; very high pH (>11) indicates alkaline ash that can raise treated water pH temporarily in new installations (requires initial backwashing). For NSF/ANSI 61 certification, third-party testing (NSF International, WQA, or equivalent accredited laboratory) verifies each batch against leachable contaminant limits.

Question 1

Coconut shell vs coal-based activated carbon — which should I choose?

Accepted Answer

Choose coconut shell for drinking water (low ash, NSF/ANSI 61, superior taste & odor removal), gold recovery CIP/CIL (highest hardness, best gold loading capacity), and small-molecule contaminants. Choose coal-based for industrial wastewater (cost-effective COD removal), VOC remediation, and high-color textile effluent (better mesopore distribution for large molecules). The fundamental difference is pore structure. Coconut shell AC (from endocarp of Cocos nucifera) develops an exceptionally uniform micropore structure during carbonization — over 90% of pore volume is micropores (<2 nm diameter). This is ideal for adsorbing small molecules (MW < 300 g/mol): taste & odor compounds (geosmin, 2-MIB, MW ~180 g/mol), chloroform and THMs (MW 119–254 g/mol), gold cyanide complex (MW ~268 g/mol). Coconut shell's high cellulose-to-lignin ratio also produces low ash content (<5%) and higher mechanical hardness. Coal-based AC (from bituminous coal) has a broader pore size distribution including mesopores (2–50 nm), making it more effective for adsorbing larger molecules: humic acids (MW 500–50,000 g/mol), textile dyes (MW 300–1000 g/mol), phenols and complex industrial organics. Price: coconut shell GAC is typically 30–50% more expensive than coal-based GAC of equivalent iodine number — justified by quality for drinking water and gold applications, but unnecessary for industrial COD removal where coal-based provides equal or better performance at lower cost.

Question 2

What is iodine number and how does it relate to adsorption capacity?

Accepted Answer

Iodine number (mg I₂ adsorbed per g AC) is the standard indicator of micropore volume and small-molecule adsorption capacity. Higher iodine number = more micropores = better removal of taste & odor, THMs, and small organics. Typical values: 800–900 mg/g (industrial), 900–1000 mg/g (water treatment), >1000 mg/g (premium drinking water / gold recovery). The iodine number test (ASTM D4607) measures how much iodine (a small molecule, MW 254 g/mol, effective diameter ~0.6 nm) is adsorbed from standard iodine solution by 0.1 g AC in a set contact time. It specifically measures micropore volume (pores accessible to I₂). For drinking water taste & odor (geosmin effective diameter ~0.7 nm; 2-MIB ~0.6 nm), iodine number correlates well with removal capacity. For larger contaminants like color (humic acids, MW > 500 g/mol, effective diameter >1.5 nm) or dyes, methylene blue number (MB number) is more relevant — it measures mesopore adsorption. An AC with high iodine number but low MB number has excellent micropores but poor mesopores (typical of coconut shell) and will remove taste & odor well but remove large-molecule color poorly. For gold cyanide adsorption in CIP/CIL circuits, the gold loading capacity (kg Au / ton AC) is the operational parameter that matters — coconut shell ACs with iodine >1100 mg/g achieve 7–12 kg Au/ton vs coal-based ACs achieving 4–8 kg Au/ton. Always request the specific contaminant-relevant specification (not just iodine number) when ordering for a specific application.

Question 3

How often does GAC need to be replaced or regenerated?

Accepted Answer

Typical GAC bed life: 6–18 months in drinking water (taste & odor), 12–36 months in industrial wastewater (depends on COD load). Spent GAC can be thermally regenerated at 850–900°C (steam activation), recovering 85–95% of original adsorption capacity. Regenerated AC is 30–50% cheaper than virgin AC. Gold recovery AC is regenerated by acid stripping (elution) and kiln reactivation every 3–4 weeks. GAC bed life depends on contaminant loading rate and breakthrough criterion. In drinking water taste & odor control, the breakthrough criterion is typically when outlet geosmin/MIB > 5 ng/L (human odor threshold ~5–10 ng/L). Bed life is influenced by: (1) influent geosmin/MIB concentration (seasonal peaks of 50–200 ng/L in algae-affected reservoirs vs stable <20 ng/L in groundwater); (2) empty bed contact time (EBCT — longer EBCT gives longer life; standard design 10–20 min EBCT); (3) natural organic matter (NOM) competition — NOM competes with target micropollutants for micropores and is the main cause of premature breakthrough in surface water. For industrial COD removal, breakthrough is when outlet COD > discharge limit (typically 50–100 mg/L). At 100 mg/L influent COD and 10 mg/L outlet target, a well-designed GAC column lasts 2–4 months per service; at 500 mg/L influent COD, 2–4 weeks. Most industrial operators run two columns in series (lead-lag) to maximize utilization — when the lead column exhausts, the lag column becomes the lead, and the exhausted column is taken offline for regeneration or replacement. Thermal regeneration economics: for GAC consumption > 10 ton/month, thermal regeneration (¥3,000–6,000/ton) vs virgin AC replacement (¥8,000–15,000/ton) gives 3–5 year payback on a rotary kiln regeneration system.

Question 4

What mesh size should I specify for my GAC filter?

Accepted Answer

Standard water treatment GAC sizes: 8×30 US mesh (0.6–2.4 mm, most common for gravity and pressure filters), 12×40 mesh (0.4–1.7 mm, tighter packing, lower flow rate), 4×8 mesh (2.4–4.8 mm, high-flow industrial, lower pressure drop). For gold CIP/CIL: 6×16 mesh (1.2–3.4 mm, large size to prevent screen blinding). Particle size affects pressure drop, contact time, and backwash requirements. Smaller particles give more external surface area per unit volume (better kinetics) but higher pressure drop across the bed and more frequent backwashing to prevent channeling. The Carman-Kozeny equation predicts that pressure drop scales with the square of (1/d_p) — halving particle size quadruples pressure drop at the same flow velocity. Standard drinking water GAC filters use 8×30 US mesh (effective size 0.6–0.8 mm, uniformity coefficient <1.9) — this balances pressure drop (<3 m head per meter bed depth at 10 m/h loading rate) with adequate EBCT. For rapid filter applications with high hydraulic loading rates (20–30 m/h), 4×8 mesh reduces pressure drop but increases EBCT requirement. Finer 12×40 mesh gives better kinetics for fast-diffusing compounds but requires more careful hydraulic design and more frequent backwash (at least 15 L/min·m² to fluidize 40% bed expansion). For filter design, always specify: effective size (ES), uniformity coefficient (UC), iodine number, ash content, moisture content, and whether NSF/ANSI 61 certification is required.

Question 5

What documents are available — COA, test certificates?

Accepted Answer

Standard COA includes: iodine number (ASTM D4607), methylene blue number, moisture content, ash content, hardness number (ASTM D3802), pH, and particle size distribution. Drinking water grades: NSF/ANSI Standard 61 certification per batch. Gold recovery grades: gold adsorption capacity test (Mintek or equivalent). Vapor phase grades: CTC activity (ASTM D3467), apparent density. Activated carbon COA parameters and their significance: Iodine number (ASTM D4607) — primary indicator of micropore volume; test measures mg I₂ adsorbed by 1g AC from 0.1N I₂ solution; minimum specs: 900 mg/g for water treatment, 1000 mg/g for drinking water. Methylene blue (MB) number — indicates mesopore volume; minimum 150 mg/g for general water treatment, >200 mg/g for color removal. Moisture content — should be <5% for granular, <10% for powder; high moisture reduces effective adsorption capacity and indicates storage problems. Ash content — inorganic residue after 900°C combustion; low ash (<5%) is essential for drinking water; high ash (>15%) indicates coal-based with high mineral content, which affects adsorption selectivity. Hardness number (ASTM D3802 ball-pan hardness) — measures resistance to abrasion in standard tumbling test; gold recovery carbon requires ≥97% hardness; drinking water GAC requires ≥90%; industrial GAC ≥85%. pH (slurry) — should be 7–10 for most applications; very high pH (>11) indicates alkaline ash that can raise treated water pH temporarily in new installations (requires initial backwashing). For NSF/ANSI 61 certification, third-party testing (NSF International, WQA, or equivalent accredited laboratory) verifies each batch against leachable contaminant limits.

Application	Carbon Type	Form	Key Specification	Recommended Grade
Drinking water GAC filter (taste & odor)	Coconut shell GAC	8×30 mesh granular	Iodine ≥1000 mg/g, hardness ≥95%	drinking-water-ac
Municipal water turbidity event (PAC emergency dose)	Wood-based PAC	200 mesh powder	MB ≥180 mg/g, rapid dispersion <30 s	wood-based-pac
Industrial wastewater COD removal (GAC column)	Coal-based GAC	4×8 or 8×30 mesh	Iodine ≥900 mg/g, hardness ≥90%	wastewater-cod-ac
Gold recovery CIP/CIL	Coconut shell GAC (gold grade)	6×16 mesh, high hardness	Gold adsorption capacity ≥7 kg Au/t AC, hardness ≥98%	coconut-gold-recovery
VOC / solvent vapor recovery	Coal columnar AC	3mm or 4mm pellets	CCl₄ activity ≥60%, hardness ≥95%	coal-columnar-ac
H₂S / odor control (impregnated)	Impregnated AC (KOH or KMnO₄)	4mm pellets	H₂S capacity ≥150 mg/g, break through test	impregnated-ac
High-color industrial WW (textile / dye)	Coal-based GAC, mesoporous	8×30 mesh	MB ≥200 mg/g for color removal	coal-based-gac
Small water supply (household / hotel)	Coconut shell GAC compact	8×30 or 12×40 mesh	NSF/ANSI 61, low ash <5%	coconut-shell-gac

International Brand Grade	China Equivalent	Major Chinese Producers
Calgon Carbon Filtrasorb 400 (coal 8×30 mesh)	Coal-based GAC 8×30 mesh, iodine 900–1000 mg/g	宁夏华辉、大同煤基炭、山西新华炭素
Jacobi AquaSorb 1000 (coconut 8×30 mesh)	Coconut shell GAC 8×30 mesh, iodine ≥1000 mg/g	福建闽清坤达、广西绿城、山东华格
Norit (Cabot) GAC 830 (coal granular)	Coal-based GAC iodine 850 mg/g, industrial grade	宁夏华辉、内蒙古日盛
Jacobi GoldSorb (coconut CIP/CIL gold)	Coconut shell GAC gold grade 6×16 mesh, hardness ≥98%	福建闽清坤达、广西绿城活性炭
Norit PAC W35 (wood PAC 200 mesh)	Wood-based PAC 200 mesh, MB ≥200 mg/g	江西鑫通炭素、山东华格
Kuraray GW (coconut GAC, drinking water)	Coconut shell GAC NSF/ANSI 61, iodine ≥1100 mg/g	福建闽清坤达、广西绿城
Sabre (columnar 3mm coal pellet)	Coal columnar AC 3mm, CTC ≥65%	宁夏华辉、大同煤基炭
Hopkalite / Puralite (KMnO₄ impregnated)	KMnO₄ impregnated AC 4mm pellets	宁夏嘉翔、北京金阳

Activated Carbon Selection Guide — GAC, PAC, Coconut Shell, Coal-Based for Water Purification & Gold Recovery

Quick-Pick by System

All Grades (by chemistry class)

Coconut Shell GAC — Drinking Water & Gold Recovery(3)

Coconut Shell Granular Activated Carbon

Activated Carbon for Drinking Water

Coconut Shell Activated Carbon (Gold Recovery)

Coal-Based GAC — Industrial & High-Hardness Applications(2)

Coal-Based Granular Activated Carbon

Activated Carbon for Wastewater COD Removal

Wood-Based PAC — Rapid Adsorption, Emergency Dosing(1)

Wood-Based Powdered Activated Carbon

Columnar / Extruded AC — Vapor Phase & Solvent Recovery(1)

Coal-Based Columnar Activated Carbon

Impregnated AC — H₂S, Mercury, Specialty Gas Removal(1)

Impregnated Activated Carbon (H2S/Mercury Removal)

Imported Brand → China Equivalent

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