Correlations among factors of sulfide ores in oxidation process at ambient temperature

Vol. 14 No. 1Trans. Nonferrous Met. Soc. ChinaFeb. 2004Article ID: 1003 - 6326(2004)01 -0175 - 05Correlations among factors of sulfide ores in oxidation processat ambient temperatureWU Chao(吴超)， LI Zi-jun(李孜军)，ZHOU Bo(周勃)(School of Resources and Safety Engineering, Central South University, Changsha 410083, China)Abstract: Spontaneous combustion is one of the serious problems in the mining of sulfide ore deposits. The rele-vant factors, e. g. oxygen absorption quantity, mass increase, contents of water soluble iron ions and sulfate ion ofsulfide ore samples in the oxidation process were investigated both in theory and experiment. The results from theinvestigation show that there is no general interpretation relation among the oxygen absorption quantity， the con-tents of sulfate ion and water soluble iron ions during the oxidation process of sulfide ores at ambient temperature.However, there is a linear relationship between the mass increase of the sulfide ore samples in the oxidation processat ambient temperature and the quantity of oxygen absorption. Therefore, the simple and cheap mass scaling methodis suitable for predicting the oxygen absorption performance of sulfide ores;at ambient temperature in place of the ex-pensive and complicated chemical method used hitherto. Furthermore, combined with other items of breeding firetest, the mass increase potential can also be used to predict the spontaneous combustion tendency of sulfide ores.Key words: sulfide ore; oxidation absorption; oxidization products; spontaneous combustion; mass increase scal-ing method; combustion predictionCLC number: TD75Document code: AINTRODUCTIONmethod, which includes: 1) geological investiga-tion; 2) ore sampling; 3 ) mineralography andIt is well known that spontaneous combus-chemical analysis; 4) ore sample crushing anction，premature detonation and dust explosion arephysical parameter test; 5measurements of massserious problems when mining sulfide ore depos-increase, water soluble iron ions， sulfate ion， pHits-6. For example， outbreak of fire from thevalue，rate of oxygen absorption, critical tempera-spontaneous combustion of sulfide ores in a mineture of accelerating self-heating，ignition point; 6can produce large quantities of toxic gases and in-in-situ investigation of sulfide ore type distribu-tense heat, which pollutes the working environ-tion，mining condition analysis; 7 ) risk assess-ment，and may lead to big economic losses as wellment; 8) control examination if necessary. Amongas loss of life. Therefore, it is very important to e-the investigation items of this schedule, some com-valuate the potential for spontaneous combustionplicated and costly chemical analysis methods areof sulfide ores before designing and mining the orerequired, particularly the testing of oxygen absorp-deposits. At present，the mechanism of spontane-tion. From an economic stand point, it will be veryous combustion commonly accepted is that sulfidesignificant if a simple and cheap test method can beores undergo a slow oxidation process when ex-devised in lieu of the chemical one.posed to moist air at ambient temperature, with e-mission of heat，gases and moisture. If the heatTHEORETICAL ANALYSISgenerated does not dissipate， it will increase thetemperature of sulfide ores， and as the result theAt ambient temperature, sulfide ores can reactrate of oxidation will increase. If it proceeds un-with oxygen and water in a given environment. Forcheckedly, it can eventually result in the ignition ofpyrite, the main reactions are as follows1.19]:sulfide orestl. Hence, it is very significant to esti-2FeS2十7O2十2H2O= 2FeSO4十2H2 SO,mate the oxidation potential of sulfide ores and toQ=-2 558.4 kJ .invent the effective controlling ways. There are4FeS2 + 15O2 + 14H2O= 4Fe(OH)3+ 8H2 SO,several methods which are applicable for this pur-Q=-5092 kJ .pose-19. However, all these methods are compli-中国媒化rFeO.+8H:SO,cated and involve costly chemical analysis. For ex-ample，Ref. [7] described a complex asssingMHC N M H Ghe important reactions①Foundation item: Project( 95- 116-01-03-03) supported by the Ministry of Science and Technology，ChinaReceived date: 2003 - 02 - 26; Acepted date: 2003 -07 -08Correspndeanes带u Chao, Professor, PhD; Tel: +86-731-8876524; E mail: wuchao@ mail. csu. edu. cn●176●T rans. Nonferrous Met. Soc. ChinaFeb. 2004are as follows:Table 1 Chemical composition of selected sulfide2Fer S。+31O2 + 2H2O= 14FeSO. +2H2 SO,ores in MINE1(mass fraction, %.Q=- 12 590.0 kJ(4)2FeS+ 8H2O+4O2 =Sample Main sulfideOtherTotalTotal iron .sulfNo.mineralscontentFeSO.●H2O+ FeSO●7H2Ominerals contentQ=-1771.3 kJ(5)FeS 95%CuFeS2 1% 35. 3456. 7412FeSO4 +6H2O+ 3O2=4Fe2 (SO):+ 4Fe(OH):2FeS2 45%,CuFeSz 1% 44. 0145. 37Fes 38%Q=-762.5 kJ .(6)From Eqns. (1)-(6)，it can be seen that at4FeS 96.5% CuFeS2 0.5% 36. 0356.89ambient temperature, no SO2 gas or other volatile .matter is released, and therefore, the mass of theFeS2 20%，CuFeS2 1% 38. 31sulfide ores will increase with increasing oxidationFeS 72%time.' The more active the sample is, the larger theFeS. 66%，CuFeS, 3%，28.2243.57mass increase in the ore sample will be. A largeFeS 3%FeAsS 15%scale field experiment, plling ore dumps in a stope,*- Crystal size: FeS0.15- 1.0 mm; FeS2 0.2-0. 5 mm;described in Ref. [15] has proved that almost noCuFeS:0.03-0.2mmSO2 gas is released during the oxidation process ofTable 2 Chemical composition of selected sulfidesulfide ores at ambient temperature ( usually belowores in MINE2(mass fraction, %)40 C). However, can the mass scaling method beused to determine the oxidation speed of sulfide oreTotal iron，sulfidesulfursamples ? What factors can be interpreted from theminerals .minerals content/content/%mass increase ? These questions should be investi-FeS, FeSCuFeS;31.5954. 5Igated in more detail by experimentation. If positive .conclusions to these questions are obtained， it willFeS，FeSCuFeS,30.3055. 63be much simpler and more economical to predictFeS，FeS CuFeS2， ZnS 32. 2656. 63the oxidation potential of sulfide ores during oxi-dization process at ambient temperature.FeS. FeSCuFeS:34. 4858. 27FeSz, FeS28. 2348.95.3 EXPERIMENTAL33. 0957. 003.1 Ore sampling3FeSz，FeSCuFeS227.2047.71To investigate the relationship among the rele-* Crystal size: Fes 0.05-0.8mm; FeS2 0. 05-0.6 mm;vant factors of sulfide ores during oxidation processCuFeS2 0. 02 -0.3 mm; Average sulfide content: FeSat ambient temperature and to solve the questions41.67%; FeS2 9. 25%; CuFeS, 3.21%pointed out above, two groups of sulfide ore sam-The selected ore samples were reduced in sizeples were collected from two mines ( Tongguangto less than 450 μm and were placed in sealed bot-shan Copper Mine and Dongguashan Copper Minetles. During the experiment, an ore sample weig-in Anhui province， China， simply described byhing 40 g was placed on an evaporation glass panMINE1 and MINE2 below). In MINE1, out of sixwith diameter of 50 mm. A group of similar oresulfide ore samples collected, one (No. 3) has nosamples were prepared and these test samples werespontaneouscombustion potential ( establishedplaced in a constant humidity chamber. The tem-subsequently through tests). In MINE2， out ofperature and relative humidity were then adjustedthirteen sulfide ore samples collected, six ( samplesto approximately 40 C and 90%，respectively.No.5，8, 9，10，11 and 12) have no spontaneousver 4 to l0d, all the tested samples were weighedcombustion potential ( established subsequentlyon an electronic scale with an accuracy of 0. 1 mg.through tests also). The main chemical composi-At the same time, the contents of the sulfate iontions and some significant properties of these oreand the water soluble iron ions in the ore samplesamples by mineralography and chemical analysiswer中国煤化工r:al apparatus7.19.. 3.2rgen absorption of oreare shown in Tables 1 and 2.MYHCNMHGn the investigation, a given mass of sulfide3.2 Test methodore sample weighing 100 g was placed in a sealed3.2. l Measurement of mass increase, water sol-container which had enough space to fill a knownuble iron ions and sulfate ion of ore sam-volume of air. The container was put in an isother-p瓦方数据mal water trough. Over a period of time， the a-Vol. 14 No. 1Correlations among factors of sulfide ores in oxidation process，177●mount of oxygen absorbed by the ore sample in thebottle was tested by an apparatus, and the totale 0.8quantity of oxygen absorbed was calculated by therelevant formula. Refs. [7, 19] had given a de▲一No.4吕0.6tailed description of the experiment and the device.*- . No.63.3 Test results品0.4The test results of the relationships betweenthe oxygen absorption quantity， mass increase,6 0.2content of water soluble iron ions， content of sul-fate ion，and oxidizing time of the ore samplesfrom MINE1 and MINE2 are shown in Figs. 1 to2004000080010.Oxidizing time/h3.0Fig.3 Content of water soluble iron ions ofNo.2ore samples from MINE1 versus oxidizing time、 2.No.4No.5. 2.0 *一No.6- No.1。1.5★- No.61.0言256”0.550100150Fig.1 Quantity of oxygen absorption by oresamples from MINE1 versus oxidizing time600800 1 000No.1Fig.4 Content of sulfate ion of ore samplesNo.z2.5from MINE1 versus oxidizing time; 2.0 *一No.63.0 r1.5.5 t◆一MINE1◆。里1.0孚2.00.5Fig.2 Mass increase of ore samples fromMINE1 versus oxidizing time0.1.5 2.0 2.5 3.0Mass increasc/%4 DISCUSSIONFig. 5 Coincidence between quantity of1) The variable tendency of the quantity of中国煤化工- mass increase ofoxygen absorption vs the oxidizing time of all sam-MINE1ples from MINE1 and MINE2 in Figs. 1 and 6 hasYHCNMHG.an obvious correlation with that of the mass in-MINE1 and MINE2 (Figs. 5 and 10). The coher-crease vs the oxidizing time shown in Figs. 2 and 7，ent coefficient reaches 0. 9 by computation.' I heserespectively. The coincidence between the oxygentest results verify that the theoretical analysis andabsorption quantity and the mass increase shows aprediction are correct. The mass increase of the orevery gooa 方数据pattern of all samples fromsamples mainly depends on absorbing oxygen from●178●Trans. Nonferrous Met. Soc. ChinaFeb. 20041.2 rNo. 1No.No.3。1.0|No.4NO.6e 0.8。一No.13富0.6/2个豆0.4上No.1).2 t名1No:2●二No4。二No.7.*- No.6 。一No.130200400600800Oxidizing time/hFig. 6 Quantity of oxygen absorption byFig. 9 Content of sulfate ion of ore samplesore samples from MINE2 versus oxidizing timefrom MINE2 versus oxidizing time●一No.16- 1一No.2●- MINE21一No.3●- No.44- No.62「是2+. No.75001 0001 5002 0002Mass increase/%Fig. 7 Mass increase of ore samples fromFig. 10 Coincidence between quantity ofMINE2 versus oxidizing timeoxygen absorption and mass increase ofore samples from MINE20.08.No.1No.6No.7No.3.No.13In the initial period of oxidation， the oxygen ab-0.06sorption quantity and the mass increase increasewith increasing oxidizing time in linear pattern.When the oxidizing time increases further， theslope of the linear curves decreases. The possiblereason for this is that a thin layer of formed prod-0.02ucts coats the surface of the ore sample. This anti-reacts the oxidation in some way，and at the sametime, the effective specific area of the ore sample is .reduced. In Figs. 6 and 7, the variation of the ox-60ygen absorption quantity vs the oxidizing time issomewhat different from that shown in Figs. 1 andFig.8 Content of water soluble iron ions of2. In the initial stage, the rate of oxygen absorp-tion and the mass increase of the ore samples areboth中国煤化工reason is that the orethe air at ambient temperature. It indicates thatsam:iginal ores， and theythe mass scaling method of the oxygen absorptionneecMYHc N M H Gperiod of time. Duringquantity of sulfide ore samples at ambient tempera-this period of pre-oxidation， some formed productsture can be used in place of the chemical test meth-are created and can accelerate the oxidation speed.od.For the samples No.2, 3, 6 and 13 of MINE2, the2) The curves in Figs. 1 and 2 can be dividedpre-oxidized period is longer than for that of theinto two瓦瓦数据according to the oxidizing time.samples No. 1，4，7 of MINE2. With the increas-Vol. 14 No. 1Correlations among factors of sulfide ores in oxidation process●179●ing of the oxidizing time，the rate of oxygen ab-Report of Investigation 8373, USA: Bureau of Mines,sorption increases quickly. However， with a fur-1979. 1-24.[7]MENG Ting-rang， WU Chao， WANG Ping long.ther increasing of oxidizing time, the rate decreasesStudy of mine spontaneous combustion of sulphide oresas demonstrated by the curves in Figs. 1 and 2.[A]. Ragula B ed. Proceedings of the US Mine Venti-3) The variation tendency of all curves inlation Symposium[C]. Salt Lake City, UT: SME,Figs.3，4, 8 and 9 bears no regular pattern. There993.203 - 207.is no coincidence among the water soluble iron ions[8] Cranney D H. Assessing the hazards of blasting in re-content，sulfate ion content and oxygen absorptionactive sulfide ores and the application of products toquantity(or mass increase) of all ore samples. Themitigate these hazards[ A]. Proceedings of 28th Annu-possible reason is that some formed products dur-al Institute on Mining Health, Safety and Research[C]. Salt Lake City: IMHSR, 1997. 111 - 117.ing the oxidation of ore samples are almost water[9] Pahlman J E，Reimers G W. Thermal gravimetric a-insoluble according to Eqns. (1) to (6)，e.g. Fe2+nalysis of pyrite oxidation at low temperature[R]. Rein Fe2(SO4)z, Fe(OH)3，Fe2O3.port of Investigations 9059， USA: Bureau of Mines,1986. 1 - 15.5 CONCLUSIONS[10] Rosenblum F，Spira P. Evaluation of hazard fromsel- heating of sulfide rock[J]. CIM Bull, 1995，88At ambient temperature, the quantity of oxy-(989): 44- 49.gen absorption of sulfide ore samples during oxida-[11] Steis T E W. Sulfide ore/ explosives exothermic reac-tions[J]. CIM Bull, 1995， 87(987): 54 -57.tion process can be tested by mass scaling method[12] William H. Spontaneous combustion fire detection forbecause the coincidence between these factors is inmetal mines[R]. Information Circular 9144， USA:linear pattern with good inherent coefficient.Bureau of Mines, 1987. 1 - 25.However, the water soluble iron ions content, sul-[13] WU Chao. Fault tree analysis of spontaneous com-fate ion content and oxygen absorption quantity (or .bustion of sulphide ores and its risk assessment[J].mass increase) have no inherent correspondenceJournal of Central South University of Technology ，with each other.1995，2(2): 77 - 80.[14] WU Chao， MENG Ting -rang. Safety assessmenttechnique for the spontaneous detonation of explo-ACKNOWLEDGEMENTsives in the mining of sulphide ore deposits[J]. Min-The authors are greatly indebted to Professoring Technology, 1996, 78(902): 285 - 288.Gour Sen of Wollongong University in Australia[15] WU Chao, WANG Ping-long. MENG Ting rang. Infor editing this paper.situ measurement of breeding-fire of sulphide oredumps[J]. Trans Nonferrous Met Soc China，1997.REFERENCES7(1): 33 - 37.[1] Ninteman D J. Spontaneous oxidation and combustion[16] Pomroy W H. Spontaneous combustion fire detectionfor deep metal mines[ R]. Information Circular 9144,of sulfide ores in underground mines[R]. 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