Coal gangue ni solid waste inayobaki baada ya coal mining na washing operations, na inaweza kuwa na residual coal na sulfur-bearing compounds pamoja na mineral matter. Inapohifadhiwa kwa muda mrefu katika open air, rainwater inaweza kupita ndani ya gangue pile, kuyeyusha minerals, kubadilisha pore structure na kugeuza chemical groups kwenye surface. Utafiti huu umechunguza jinsi dynamic leaching inayosimulate rainfall inavyoathiri low-temperature oxidation na spontaneous-combustion tendency ya high-sulfur coal gangue.

Samples kutoka coal mine katika Shanxi province zilileachwa kwa pure water kwa 3, 6, 12, 24, 48 na 96 days. Katika separate experimental group, samples zili-exposewa kwa pH 7, pH 5 na pH 4 solutions kwa six days. Pore structure ilitathminiwa kwa low-temperature N₂ adsorption, surface chemistry kwa FTIR, gas formation kwa temperature-programmed oxidation, mass na heat changes kwa TG-DSC, na energy barriers kwa Coats–Redfern kinetic analysis.

Results zilionyesha kwamba effect ya leaching haikuwa linear. Pore network na specific surface area zilianza kuendelea, zikafikia highest level karibu 48 days, kisha zikapungua kwa longer leaching kutokana na collapse ya large pores na filling kwa fine precipitates. Specific surface area ilifikia 9,323 m²/g katika 48 days. Average pore diameter, iliyokuwa 45,44 nm katika raw sample, ilishuka hadi 38,71 nm baada ya 96 days.

Hydroxyl, oxygen-containing na aromatic hydrocarbon groups pia zilifikia highest level katika 48 days. FTIR peak areas za groups hizi tatu zilifikia 8,7, 10,2 na 7,6 times raw sample mtawalia. Aliphatic hydrocarbon groups zilifika peak mapema zaidi, katika 24 days.

Pore development na increase ya reactive surface groups ziliharakisha oxygen transport ndani ya gangue particles na low-temperature oxidation. Katika 48-day sample, crossing-point temperature ilishuka hadi 168,4 °C, total heat release iliongezeka hadi 733,1 J/g, na apparent activation energy katika oxygen-adsorption stage ikashuka hadi 72,53 kJ/mol. Energy barrier hii ni takribani %64 ya raw-gang value.

Weakly acidic pH 5 solution iliimarisha low-temperature oxidation kidogo kuliko pure water kwa kuongeza hydroxyl na carboxyl groups. Kwa upande mwingine, strong acid katika pH 4 ilisababisha dissolution au degradation ya reactive organic structures na surface groups; total heat release ikashuka hadi 608,0 J/g, chini ya raw-sample value ya 624,6 J/g.

Utafiti unaonyesha kwamba rain na acidic seepage water zinaweza kuathiri fire risk katika coal-gangue piles si kwa kuongeza moisture pekee, bali kwa kubadilisha pores, oxygen transport, surface chemistry na reaction kinetics kwa pamoja. Hata hivyo, experiments zilifanywa katika laboratory columns. Temperature gradients, microbial activity, irregular rainfall, airflow na moisture transport katika real piles hazikumodeliwa moja kwa moja.

Kwa nini coal gangue inaweza kujiwasha yenyewe?

Coal gangue haijaundwa kabisa na noncombustible mineral matter. Inaweza kuwa na residual coal, fixed carbon, volatile organic compounds na sulfur-bearing minerals kama pyrite. Components hizi zinaweza kureact polepole na atmospheric oxygen na kuzalisha heat.

Ikiwa heat inayozalishwa na pile haiwezi kuhamishwa kwa environment haraka vya kutosha, temperature huongezeka taratibu. Oxidation inayoanza katika low temperature inaweza kuharakishwa baada ya critical temperature kupitwa, na long self-heating period inaweza kutokea kabla ya visible flame kuonekana.

Composition ya raw gang sample iliyochunguzwa katika study ni muhimu kwa risk hii:

Ingawa high ash fraction inaonyesha sehemu kubwa ya sample ni mineral matter, %26,28 fixed carbon, %14,32 volatile matter na %6,529 sulfur vinaonyesha kiasi kikubwa cha reactive components kwa oxidation na heat generation.

Leaching ina maana gani?

Leaching ni process ambayo water inapopita ndani ya solid material huyeyusha na kubeba soluble minerals, ions na chemical products. Katika open-air gangue piles, rainwater huingia kutoka upper surface, husafiri kwenye spaces kati ya particles na hutoka chini ya pile kama seepage water.

Process hii inaweza kuleta changes zinazokinzana katika structure ya gangue:

• Dissolution ya carbonate na clay minerals inaweza kuunda new voids na cracks.
• Connection ya closed pores inaweza kurahisisha oxygen passage.
• Mineral coating inayofunika organic structures inaweza kuondolewa na kufichua reactive carbon surfaces.
• Water na oxygen zinaweza kuongeza formation ya active groups kama hydroxyl, carbonyl na carboxyl.
• Very long-term au strongly acidic leaching inaweza kusababisha dissolution ya reactive structures na collapse ya large pores.

Kwa hiyo haitoshi kudhani kwamba rain inalowesha gangue pekee au huipoza katika every condition. Baada ya water kutoka na sample kukutana tena na air, changed pore structure inaweza kusababisha stronger oxygen transport.

Swali kuu la utafiti ni lipi?

Watafiti walijaribu kueleza relations tatu ndani ya study moja:

1. Leaching duration na solution pH hubadilishaje pore structure?
2. Change hii hugeuzaje reactive functional groups kwenye gangue surface?
3. Transformation katika pore na surface chemistry inaakisiwa vipi katika oxygen consumption, gas formation, heat release na spontaneous-combustion kinetics?

Previous studies nyingi zilitegemea static immersion experiments ambako samples zilizamishwa kikamilifu ndani ya water kwa certain period. Lakini katika real rainfall, water badala ya kukusanyika continuously husafiri kupitia material. Dynamic dripping system ya study ililenga kuwakilisha flow hii katika laboratory scale.

Samples ziliandaliwaje?

Gangue samples zilichukuliwa kutoka coal mine katika Xinzhou region, Shanxi province, China. Ili kupunguza premature reaction with oxygen, samples zilicrushwa, kugrindwa na dry-sieved chini ya inert atmosphere.

Four particle groups ziliandaliwa:

Kila particle-size class iliainishwa separately, ikawekwa katika airtight containers na kuhifadhiwa closed hadi experiments.

Dynamic leaching experiment iliundwaje?

Experimental setup ilikuwa na custom-made dripping device, flow regulator, leaching tubes, funnels, support plate na waste-liquid collection tank. Transparent acrylic columns zilikuwa na inner diameter 53 mm, outer diameter 55 mm na height 15 cm.

Takribani 2 cm quartz sand iliwekwa kwenye base ya kila column. Juu yake, 25 g kutoka kila four particle class iliwekwa from smallest to largest. Hivyo total gang used katika one column ilikuwa takribani 100 g.

Kwa kutegemea annual average rainfall ya Xinzhou, total annual leaching volume ilikubaliwa kuwa 999 mL. Katika kila application, 83 mL solution ilitolewa kwenye column kwa rate ya 1 mL/min na process ikarudiwa every 24 hours.

Experimental groups ni zipi?

Samples baada ya leaching ziliachwa air-dry kwenye trays kwa 48 hours, kisha zikadry under vacuum at 40 °C kwa 48 hours. Hivyo direct effect ya free water katika subsequent oxidation experiments ilipunguzwa na permanent structural changes caused by leaching zikachunguzwa.

Pore structure ilipimwaje?

Takribani 0,8 g kutoka kila sample ilichambuliwa katika Autosorb-iQ physical adsorption instrument. Kabla ya measurement, samples zilidegas under vacuum at 80 °C kwa 12 hours.

• Adsorbed gas: Nitrogen
• Measurement temperature: 77 K
• Relative pressure range: P/P₀ = 0,001–0,995
• Adsorption points: 30
• Desorption points: 30
• Specific surface area: BET model
• Total pore volume: BJH model
• Pore-size distribution: DFT model

Adsorption curves zinaonyesha nini?

Nitrogen adsorption-desorption curves za all samples zilikuwa Type IV(a) kwa IUPAC classification. Shape hii inaonyesha structure ni predominantly mesoporous na inaweza pia kuwa na micropore contribution.

P/P₀ ikiwa katika 0–0,4 range, nitrogen molecules zilijaza small pores na adsorbed amount ikaongezeka nonlinearly. Baada ya takribani 0,4, adsorption na desorption branches zilitengana.

H2(a)-type hysteresis loop iliyoonekana kwenye curves inaonyesha “ink-bottle” pores. Katika pores hizi inner cavity ni wide lakini neck inayoelekea nje ni narrow. P/P₀ ikizidi 0,9, adsorbed nitrogen amount iliongezeka rapidly kutokana na capillary condensation.

Pore network ilibadilikaje kwa muda?

Leaching duration ilipoongezeka, specific surface area na total pore volume ziliongezeka kwanza, zikafikia maximum katika 48 days, kisha zikapungua. Highest specific surface area ilipimwa kuwa 9,323 m²/g.

Average pore diameter kwa ujumla ilipungua:

• Raw gang: 45,44 nm
• 96-day sample: 38,71 nm

Katika Figure 4, yellow bars zinaonyesha total pore volume, orange bars specific surface area, na blue line average pore diameter. Rise ya bars na decline ya blue line katika 24–48-day samples inaunga mkono formation ya many smaller micro- na mesopores badala ya large voids.

Early and middle period: pore opening

Between 12–48 days, soluble carbonates na baadhi ya clay minerals ziliondolewa, cracks zikapanuka na closed voids zikaunganishwa. Formation ya new micro- na mesopores iliongeza surface area inayoweza kukutana na oxygen.

Late period: pore narrowing and filling

Between 48–96 days, prolonged water passage ilisababisha collapse ya some large pores, huku transported fine particles zikijaza voids partially. Kwa hiyo surface area na total volume zilipungua na average pore diameter ikapungua zaidi.

Hata hivyo, specific surface area ya 96-day sample bado ilikuwa higher than raw gang. Hivyo late-stage decline haimaanishi structure imerudi kabisa kwenye initial condition.

Acidity iliathirije pores?

Acidic solutions ziliharakisha dissolution ya minerals kama carbonates, zikaongeza specific surface area na total pore volume huku zikishusha average pore size. Study inaona weakly acidic conditions hasa kama zinazozalisha many small pores.

Lakini increase ya pore number peke yake haiamui spontaneous-combustion risk. pH pia ilibadilisha organic functional groups kwenye surface na kutoa different chemical outcomes kati ya pH 5 na pH 4.

FTIR analysis ilifanywaje?

Surface chemistry ya samples ilichunguzwa kwa VERTEX 80V FTIR spectrometer. Gangue na KBr zilichanganywa kwa mass ratio 1:180 na kushikiliwa chini ya 20 MPa pressure kwa 10 minutes ili kutengeneza pellets.

• Wavenumber range: 400–4.000 cm⁻¹
• Spectral resolution: 4 cm⁻¹
• Number of scans: 32
• Peak-deconvolution software: PeakFit

Four spectral regions zilitathminiwa separately:

Functional groups zilibadilikaje kwa muda?

Four main functional groups zote ziliongezeka kwanza kisha zikapungua. Hata hivyo, peak times hazikuwa sawa:

Katika first 48 days, combined effect ya water na oxygen iliongeza surface oxidation. Hydroxyl groups ziliundwa kupitia alcohol na phenol structures; baadhi yake zikabadilika kuwa oxygenated structures kama ester, ether, aldehyde na carboxyl.

Katika same period, oxygen ilishambulia aromatic skeletons, ikavunja some C–C bonds na kuunda more reactive fragments. Swelling caused by water film ilipunguza steric hindrance kati ya aliphatic chains na aromatic cores na kurahisisha breakdown ya long aliphatic chains.

Between 48–96 days, secondary oxidation ilikuwa largely complete, soluble oxidation products zikaondolewa na flow, na degradation ya aromatic structures ikaendelea. Kwa hiyo functional-group amounts zilipungua, lakini hata katika 96-day samples zilibaki above raw-gang level.

Kwa nini functional groups zinaathiri fire risk?

Oxygenated groups kama hydroxyl, carbonyl na carboxyl ni active centers zinazoweza chemically bind oxygen katika low temperatures. Oxygen adsorption kwenye sites hizi inaweza kuunda unstable peroxide intermediates na free radicals.

Decomposition ya intermediates hizi huzalisha new radicals na heat, na ku-support chain oxidation reactions. Pores huunda physical pathway ya oxygen transport, huku functional groups zikitoa chemical pathway ya oxygen reaction.

Study inatafsiri simultaneous increase ya oxygen-containing groups na aromatic structures kama formation ya “dual active centers”. Centers hizi mbili zinaweza kuharakisha both oxygen capture na reaction with carbon skeleton.

Kwa nini pH 5 na pH 4 zilitoa different results?

Weakly acidic pH 5

Katika pH 5 condition, amount ya hydroxyl, aliphatic hydrocarbon na oxygen-containing functional groups iliongezeka; aromatic hydrocarbon proportion ikapungua. Watafiti walieleza hili kwa accelerated formation ya alcohol, phenol na carboxyl pamoja na oxidative hydroxylation ya aromatic structures.

Surface chemistry hii iliongeza low-temperature oxygen adsorption na heat generation kidogo kuliko sample iliyoleachwa kwa pure water.

Strongly acidic pH 4

Katika pH 4 condition, total content ya all main functional groups ilishuka below raw-gang level. Strong acid ilisababisha further breakdown ya aromatic skeletons na side chains, removal ya soluble products kutoka sample na loss ya active centers.

Kwa hiyo pH 4, despite creating new pores, ilipunguza chemical sites required for oxidation na especially ikasuppress total combustion intensity at higher temperatures.

Temperature-programmed oxidation experiment ilifanywaje?

Katika kila experiment, 50 g sample iliwekwa katika ZRD-III programmable tube furnace. Sample iliheatwa kutoka 40 °C hadi 230 °C kwa 0,8 °C/min. Outlet gas ilisamplewa every 10 °C increase na kuchambuliwa kwa GC-4000A gas chromatograph.

Main indicators monitored zilikuwa:

• O₂ amount at outlet: Indicates oxygen consumption.
• CO formation: One of characteristic products of low-temperature oxidation.
• C₂H₄ formation: Provides information on breakdown of organic side chains na oxidation progress.

Oxygen consumption ilibadilikaje?

During 0–48-day leaching, expanded mesopores na increased physical adsorption areas zilisababisha O₂ decline below 120 °C kuanza takribani %2–3 earlier kuliko raw sample.

Result hii inaonyesha oxygen consumption by gangue ilianza katika lower temperature. Pore network ilirahisisha oxygen transport huku increased active groups zikiharakisha chemical adsorption.

Katika 96-day sample, oxygen consumption ilipungua kutokana na functional-group loss na outlet O₂ ikaongezeka tena. Hata hivyo, values hazikurudi fully kwenye raw-sample level; preserved mesopore network ilicompensate partially loss ya chemical activity.

CO na C₂H₄ results zinaonyesha nini?

Baada ya 48-day leaching:

• Maximum CO concentration ilifikia 1,39 times raw gang.
• CO peak temperature ilishift 15 °C lower.
• C₂H₄ initial-appearance temperature ilishuka kutoka 110 °C hadi 90 °C.
• C₂H₄ peak concentration iliongezeka takribani %18.

Changes hizi nne zinaunga mkono earlier onset na stronger progression ya oxidation katika low temperature.

Katika 96-day sample C₂H₄ onset temperature iliongezeka hadi 105 °C na CO amount ikapungua. Lakini C₂H₄ peak ilibaki above raw-gang level.

Gas formation ilibadilikaje katika acidic conditions?

Katika pH 5 condition, low-temperature O₂ consumption iliongezeka na CO production ikapanda. C₂H₄ ilianza kuonekana at 90 °C na peak concentration ilikuwa %12 higher kuliko pH 7 group.

Above 180 °C, kwa sababu reactive groups zilikuwa consumed earlier, rates of change katika O₂ na CO curves zilipungua. Kwa hiyo effect ya pH 5 ni temperature-dependent: huongeza low-temperature oxidation lakini inaweza kusababisha earlier depletion ya reactive resources at high temperature.

Katika pH 4 group, CO amount throughout entire temperature range ilibaki below pH 7 group. C₂H₄ first appeared at 110 °C na concentration ilikuwa lower kuliko neutral-leached sample. Hii inaunga mkono kwamba strong acid ilipunguza reactive side chains na functional groups.

Oxygen consumption rate at 70 °C ilihesabiwaje?

Katika paper, oxygen consumption rate at 70 °C ilihesabiwa kwa relation:

\[ R_{O_2,70}=\frac{Q_{in}\,\varphi_{in}}{22400\,S\,L}\ln\left(\frac{\varphi_{in}}{\varphi_{out}}\right) \]

Hapa:

• R_O₂,70: Oxygen consumption rate at 70 °C.
• Q_in: Inlet air flow, set at 96 mL/min.
• φ_in: Oxygen volume fraction in inlet air.
• φ_out: Oxygen volume fraction in outlet gas.
• S: Cross-sectional area of sample holder.
• L: Height of gangue layer.
• 22400: Coefficient used in conversion between gas volume and molar amount.

Outlet oxygen fraction inapopungua, logarithmic term huongezeka na calculated consumption rate hupanda.

Crossing-point temperature inaonyesha nini?

Crossing-point temperature ni integrated self-heating indicator inayowakilisha balance kati ya heat inayozalishwa na sample na heat inayopotea kwa environment. Lower temperature inaonyesha sample inaweza kuaccumulate heat earlier na kuwa more prone kwa spontaneous combustion.

Value rounded to 168 °C in abstract is given as 168,4 °C in results section.

Spontaneous-combustion index I ilitafsiriwaje?

Study inasema I index ya all samples ilikuwa kati ya 600–1.200 na ilionyesha measurable spontaneous-combustion tendency. Katika classification iliyotumiwa na study hii, lower I value ina maana higher risk.

• 48-day sample: I = 801,6; lowest value and highest risk
• 96-day sample: I = 924,1; risk decreased but remained higher than raw sample
• pH 4 sample: I = 975,7; approached raw-gang value
• pH 5 sample: approximately %7 lower I value than pH 7 control

Method note: PDF haijatoa explicit calculation equation, coefficients au classification thresholds kwa index hii. Kwa hiyo independent recalculation ya I values haiwezekani kutoka current text.

TG-DTG analysis ilifanywaje?

Approximately 10 mg sample iliwekwa katika Al₂O₃ crucible na kuheatwa katika air atmosphere kutoka 20 °C hadi 800 °C kwa 10 °C/min. Air flow iliwekwa 100 mL/min.

TG curve inaonyesha change katika sample mass, huku DTG curve ikionyesha rate ya mass loss per unit time.

Six characteristic temperatures zinawakilisha nini?

Kulingana na temperatures hizi, process ilitathminiwa katika five stages:

1. T₁–T₂: Moisture evaporation
2. T₂–T₃: Oxygen adsorption and mass gain
3. T₃–T₄: Thermal decomposition
4. T₄–T₆: Combustion
5. After T₆: Burnout

Kwa nini 24 days inajitokeza katika TG-DTG results?

T₁, T₂, T₅ na T₆ temperatures zilipungua kwanza na leaching duration, kisha zikaongezeka, na lowest levels zikaonekana katika 24-day sample. Kwa metrics hizi, 24-day sample ndiyo mfano ulioingia fastest katika oxidation-related ignition process.

Maximum mass-loss rate pia iliongezeka kwanza kisha ikapungua. Maximum mass-loss rate ya all leached samples ilikuwa higher than raw gang. Hii inaonyesha fixed carbon ili-oxidize faster katika combustion stage.

Between 0–48 days, moisture-evaporation stage ilifupishwa huku oxygen-adsorption and mass-gain stage ikirefuka. Pore development ilirahisisha kutoka kwa adsorbed water na volatile components; increase katika active groups ikaongeza reaction time with oxygen.

Je, 24-day na 48-day results zinapingana?

Hazipingani kabisa; different experiments zinapima different processes:

• Some TG-DTG characteristic temperatures were lowest in 24-day sample. Hii inaonyesha certain higher-temperature reaction stages zilitokea earlier.
• Pore area, some active functional groups, low-temperature oxygen consumption, total heat release na oxygen-adsorption activation energy reached highest-risk level in 48-day sample.

Kwa hiyo 24 days inaweza kuonekana kama point ambapo some thermal transitions occur earliest; 48 days kama point ambapo low-temperature oxidation na total heat production together are strongest. Overall conclusion ya paper inaweka highest integrated spontaneous-combustion tendency katika 48-day sample.

Acidic leaching ilibadilishaje TG-DTG stages?

Katika acid-leached samples compared with raw gang, T₂ na T₆ zilipungua, huku T₄ na T₅ zikiongezeka. Maximum mass-loss rate na total mass loss zilibaki lower kuliko pure-water-leached samples.

Acidic environment iliendeleza pore development na volatile release, na kusogeza low-temperature stages mbele, lakini kwa kuyeyusha some fixed carbon na sulfur-bearing minerals ilipunguza high-temperature combustion intensity.

Dual effect hii ilikuwa more evident katika pH 5 group, wakati pH 4 group ilikuwa more suppressive kutokana na active-component loss.

DSC curves zinaonyesha nini?

DSC ilimonitor directly heat uptake na release ya sample. All samples zilionyesha similar staged curve shapes; lakini transition from endothermic to exothermic behavior ilishift kwenda lower temperatures katika leached samples.

Below 350 °C, heat flow ya leached samples ilikuwa higher kuliko raw gang. Hii inaunga mkono enhancement ya low-temperature oxidation.

pH 5 sample ilionyesha higher heat flow kuliko pH 7 sample below 350 °C. Kwa upande mwingine, exothermic peaks above 400 °C zilipungua katika acidic samples; peak ya pH 4 sample ilishuka below raw gang.

Total heat release ilibadilikaje?

Total heat release ya 48-day sample ilikuwa 108,5 J/g, yaani takribani %17,4 higher kuliko raw sample. Katika 96-day sample value ilishuka hadi 655,2 J/g lakini ikabaki above raw-sample value ya 624,6 J/g.

pH 5 sample ilizalisha total heat ya 683,7 J/g, slightly higher kuliko 675,8 J/g ya 6-day pure-water-leached sample kwa same duration. pH 4 sample value ya 608,0 J/g ilikuwa below raw gang.

Oxidation kinetics zilihesabiwaje?

Activation energy na pre-exponential factor zilihesabiwa kwa Coats–Redfern equation:

\[ \ln\left[\frac{G(\alpha)}{T^2}\right]=\ln\left(\frac{AR}{\beta E}\right)-\frac{E}{RT} \]

Hapa:

• G(α): Selected reaction-mechanism function.
• α: Conversion fraction.
• T: Absolute temperature, K.
• R: Universal gas constant, 8,314 J·mol⁻¹·K⁻¹.
• A: Pre-exponential factor, min⁻¹.
• β: Heating rate, K/min.
• E: Apparent activation energy, kJ/mol.

Katika linear fitting ya equation, slope inahusiana na −E/R. Lower activation energy ina maana lower energy barrier kwa reaction initiation na stronger low-temperature oxidation tendency.

Je, reaction mechanism ilibadilika kwa leaching?

Watafiti walijaribu nine common gas–solid reaction mechanism functions na kuchagua best fit kwa kila stage.

Transition ya oxygen adsorption kutoka first order hadi 1,5 order inaonyesha kwamba kwa prolonged leaching reaction ilitegemea zaidi si number ya chemical sites pekee bali pia oxygen transport katika pore network.

Activation energy ilibadilikaje?

Katika oxygen-adsorption and mass-gain stage, activation energy ya all leached samples ilikuwa lower kuliko raw gang. Lowest value ilipimwa katika 48-day sample:

E = 72,53 kJ/mol

Value hii ni takribani %64 ya raw-gang energy barrier. Kwa maneno mengine, baada ya 48-day leaching apparent energy barrier required to initiate low-temperature oxidation ilipungua takribani %36.

Activation energies katika pyrolysis stage zilibaki katika narrow range ya 79,01–83,29 kJ/mol. Result hii inaonyesha leaching iliathiri pyrolysis stage kwa kiwango kidogo na stage hii ilidhibitiwa hasa na temperature.

Activation energy katika combustion stage iliongezeka kwanza na duration, ikafikia maximum at 48 days na ikapungua at 96 days. Increase hii haimaanishi low-temperature oxidation ilidhoofika. Study inaona increase ya oxygenated na aromatic structures kutokana na leaching ikifanya structures hizi kushiriki zaidi katika combustion stage na kubadilisha apparent energy demand at high temperature.

Proposed integrated mechanism ni ipi?

1. Mineral dissolution and pore restructuring

Water huyeyusha carbonates na clay minerals na kuunda voids na cracks. Connection ya previously closed pores inarahisisha oxygen transport kwenda deeper regions ya gangue particles.

2. Exposure of reactive organic surfaces

Mineral coatings zinapoondolewa, organic carbon structures zilizokuwa chini ya mineral layers zinakutana directly na atmospheric oxygen.

3. Formation of active functional groups

Water–oxygen interaction huvunja weak bonds katika aliphatic side chains na coal skeleton. Oxygen-containing groups kama −OH, C=O na −COOH huongezeka.

4. Chemical oxygen adsorption

Active groups hufunga oxygen katika low temperature na kuunda unstable peroxides na free radicals. Process hii hushusha energy barrier ya oxidation chain reactions.

5. Heat accumulation

Better oxygen transport na faster surface reactions hufanya kazi pamoja kuongeza oxygen consumption, CO na C₂H₄ formation na total heat release.

6. Decline under excessive leaching

Leaching ikizidi critical duration, pore collapse, filling with fine particles na loss ya reactive organic products huanza. Strong acid pia hupunguza active carbon skeletons na functional groups. Hivyo oxidation activity hupungua; lakini kwa kuwa pore structure hubaki more developed kuliko initially, risk haiondoki kabisa.

Hii ina maana gani kwa early warning na field management?

Study inaonyesha kuwa kuangalia high-moisture period immediately after rainfall pekee haitoshi. Baada ya water kutoka kwenye pile na material kukauka tena, more open pore network na more reactive surface chemistry vinaweza kubaki.

Laboratory results zinaonyesha hasa period after medium-duration leaching inapaswa kufuatiliwa. Hata hivyo, 24- au 48-day thresholds haziwezi kutumika directly kwa all field piles. Real timing inaweza kubadilika kwa rainfall amount, particle size, pile height, air permeability, temperature, pyrite content na drying rate.

Katika mechanism-based early-warning approach, indicators zifuatazo zinaweza kufuatiliwa pamoja:

• Internal pile temperature na temperature-rise rate
• Decrease ya O₂ katika outlet air
• Appearance ya characteristic gases kama CO na C₂H₄
• pH ya seepage water
• Drying time after rainfall
• Airflow na permeability ndani ya pile

Study haikutest monitoring system hii field; imetoa mechanistic data tu kuhusu physical na chemical variables zinazoweza kuwa meaningful kwa early warning.

Nguvu za utafiti ni zipi?

• Dynamic dripping-column system inayosimulate rainfall flow ilitumika badala ya static immersion.
• Wide duration range ya 3–96 days iliruhusu pore development na late-stage decline zote kuonekana.
• Comparison ya pH 7, pH 5 na pH 4 ilitenganisha effects za weak na strong acid.
• Pore structure, surface chemistry, characteristic gases, thermal behavior na kinetic energy barriers zilichunguzwa katika same experimental sequence.
• Raw sample na treatment groups zote zilipitia same drying procedure.
• Total heat release ilihesabiwa quantitatively kwa DSC.
• Separate kinetic mechanisms zilitathminiwa kwa oxygen adsorption, pyrolysis na combustion stages.
• Connection kati ya pore development, active-group formation na activation energy ilielezwa kwa integrated mechanism.

Mapungufu ya utafiti ni yapi?

• Study ni preprint ambayo haijapitia peer review.
• Experiments zilifanywa katika 15 cm-high laboratory columns badala ya real gangue pile.
• Temperature gradients, airflow, compaction, irregular particle distribution na moisture migration katika real piles hazikuwakilishwa directly.
• Microbial activity na real acid-mine drainage yenye different ions hazikuchunguzwa.
• High-sulfur gangue kutoka single mine site pekee ilitumika.
• Number of experimental replicates haikutajwa.
• Graphs hazina error bars, standard deviations au confidence intervals.
• No statistical significance tests between groups were reported.
• No in situ microscopic imaging directly demonstrating causal relation between pores and functional groups was performed.
• pH experiments zilifanywa kwa six-day leaching pekee; full pH-duration interaction haikuchunguzwa.
• No explicit calculation equation for spontaneous-combustion index I was given.
• Dissolved minerals na elements katika leachate hazikuripotiwa kwa undani.
• Experiment ilitegemea regular dripping every 24 hours; duration na intensity variability ya real rainfall haikuwakilishwa.
• Results hazijavalidatewa against field-scale fire onset au actual ignition time.

Matokeo yanayoungwa mkono na utafiti

• Dynamic leaching ilibadilisha significantly pore network ya studied high-sulfur gangue.
• Specific surface area na pore volume ziliongezeka hadi 48 days na kisha zikapungua.
• Hydroxyl, oxygenated na aromatic groups zilifikia maximum at 48 days.
• All leached duration groups zilionyesha higher low-temperature oxidation activity kuliko raw sample.
• 48-day sample ilikuwa na lowest crossing-point temperature, highest total heat release na lowest oxygen-adsorption activation energy.
• Weakly acidic pH 5 iliimarisha low-temperature oxidation kidogo kuliko neutral leaching.
• Strongly acidic pH 4 ilipunguza active functional groups na total heat release.
• Very long leaching ilipunguza risk lakini haikurudisha sample completely kwenye raw-gang level.

Matokeo ambayo utafiti hauthibitishi

• Haijathibitishwa kwamba all coal-gangue types hufikia highest risk exactly after 48 days.
• Haiwezi kusemwa kwamba every acidic rainfall au seepage water huongeza fire risk.
• pH 4 treatment haijaonyeshwa kuwa safe au applicable field fire-prevention method.
• Laboratory-measured 168,4 °C haiwezi kutumika directly kama ignition temperature ya real gangue pile.
• Haiwezi kuhitimishwa kwamba rain always heats gangue piles au fire hutokea baada ya every rainfall.
• Study haikupima quantitatively heavy-metal release, field concentrations za toxic gases au human exposure.
• Proposed mechanism haijaverifywa katika low-sulfur au highly weathered gangue from different mines.
• Molecular pathway kati ya pore development na functional-group formation haikuobserviwa directly.

Mbinu na Matokeo ya Utafiti

Technical-method summary

Technical summary ya main findings

Measurements zote zikichukuliwa pamoja, highest integrated low-temperature oxidation na spontaneous-combustion tendency ilionekana katika 48-day leaching condition. Hata hivyo, some characteristic temperatures katika TG-DTG kuwa lowest at 24 days inaonyesha risk inapaswa kutathminiwa kwa multiple thermal, chemical na kinetic indicators badala ya single metric.

Maelezo ya Chanzo na Mbinu

Jina kamili asilia la utafiti: Effect of Leaching on the Oxidative Spontaneous Combustion Characteristics of Coal Gangue

Waandishi na mpangilio wao katika PDF: Yaqi Qin; Chengyue Li; Xuyao Qi; Jinhu Li; Haining Qi.

Equal first author au equal contribution: Haijatajwa katika PDF.

Corresponding author: Xuyao Qi.

Institutional affiliations:

1. Key Laboratory of Gas and Fire Control for Coal Mines, School of Safety Engineering, China University of Mining and Technology, Xuzhou, China.
2. State Key Laboratory of Coal Mine Disaster Prevention and Control, China University of Mining and Technology, Xuzhou, China.
3. School of Safety Engineering, China University of Mining and Technology, Xuzhou, China.
4. College of Safety Science and Engineering, Anhui University of Science and Technology, Huainan, China.
5. College of Safety Science and Engineering, Xinjiang Institute of Engineering, Xinjiang, China.

Author–institution mappings: Yaqi Qin, Chengyue Li and Xuyao Qi: first three institutions within China University of Mining and Technology; Jinhu Li: Anhui University of Science and Technology; Haining Qi: Xinjiang Institute of Engineering.

DOI: 10.2139/ssrn.6945186

Jarida: Hakuna peer-reviewed journal name au acceptance information katika version hii.

Publication platform: SSRN.

Original publisher: Peer-reviewed journal publisher information haikuweza kuthibitishwa. Document ni SSRN preprint record.

Document year: Inaonekana kama 2026 preprint katika SSRN bibliographic records; exact submission day haijaandikwa katika PDF.

Aina ya chanzo: Laboratory-scale preprint research article including dynamic leaching experiments, pore na surface-chemistry characterization, temperature-programmed oxidation, thermal analysis na kinetic modeling.

Peer-review status: Utafiti huu haujapitia peer review.

Official SSRN link:https://papers.ssrn.com/sol3/papers.cfm?abstract_id=6945186

DOI link:https://doi.org/10.2139/ssrn.6945186

Funding: Natural Science Foundation of Jiangsu Province (BK20240104), Science & Technology Fundamental Resources Investigation Program (2025FY101700), National Key Research and Development Program of China (2024YFC3909302) na National Natural Science Foundation of China (52574297).

Conflict of interest: Authors declared no known financial interest or personal relationship.

Data access: Data stated to be available upon request.

Makala hii ya Kituruki iliandaliwa kwa kuchunguza text, equations, experimental parameters, tables, adsorption na FTIR graphs, gas-concentration curves, TG-DTG/DSC profiles na kinetic results za PDF ya kurasa 40 iliyopakiwa. Hakuna new experimental finding, field-fire data au health-effect result iliyoongezwa kutoka nje ya PDF. External verification ilitumika tu kwa DOI na SSRN source identity.

Main limitations ni laboratory-scale experiments, examination ya only one high-sulfur gangue source, non-reporting ya experimental replicates na statistical uncertainties, lack of full factorial investigation ya pH-duration interaction, na results kutokuwa validated bado katika real gangue piles.

Preprint warning: Utafiti huu ni preprint ambayo haijapitia peer review; findings zinahitaji independent field na laboratory validation.