Document 39n7EoxeByaXD7OX3y2E67yy

JOURNAL OF THE MINE vfi' VENTILATION SOCIETY OF SOUTH AFRICA Published monthly by the Mine Ventilation Society of South Africa VOL. 41. No. 1 JANUARY, 1988 PRICE R4,50 (Excl. tax) President L.J.C. PRETORIUS Vice Presidents S.J. BLUHM AND P. DEGLON Hon. Editor R. RAMSDEN Editorial Committee Dr. R.C. BURTON, C FRITZ, R. HEMP, W. HOLDING, D. MARAIS, A.D. UNSTED Hon. Treasurer -- C.J. NISSEN Secretaries -- ASSOCIATED SCIENTIFIC AND TECHNICAL SOCIETIES OF SOUTH AFRICA, KELVIN HOUSE 2 HOLLARD STREET, JOHANNESBURG TELEPHONE 834-6198 P.O. BOX 61019 MARSHALLTOWN, TVL. The Society acknowledges, with gratitude, the financial assis tance received from the Department of National Education for the publication of the Journal. The opinions expressed by contributors do not necessarily represent the official view of the Society. Products and Services advertised in the Journal are not necessarily endorsed by the Society. Copyright 1987 by the Mine Ventilation Society of South Africa. All rights reserved. CONTENTS Composition and size of dust in a Examiners Errors., gold mine atmosphere by H.J. Annegarn, Western Branch A. Zucchiatti, J.P.F. Sellschop and B. Kusko.............. 1 Visit to Kloof.... . New Certificate for Member.............................................. 10 25 Years Ago........ . COMPOSITION AND SIZE OF DUST IN A GOLD MINE ATMOSPHERE ,11 .11 .12 H.J. Annegarn1,2, A Zucchiatti1,*, J.P.F. Sellschop1 and B Kusko2 'Wits-CSIR Schonland Research Centre for Nuclear Sciences, University of the Witwatersrand, Johannesburg 2050, 2Crocker Nuclear Laboratory, University of California, Davis CA 95616 Dust was sampled at various locations in an underground gold mine using stackedfilter units (SFUs). This device, consisting of two membrane filters in series, separates the dust aerodynamically into two fractions with a cut-offpoint at 3,0 [im diameter. Samples were analysed by particle-induced X-ray emission (PIXE). Presented are results on the chemical composition of dust in the form of composition profiles or `fingerprints' of specific dust-generating localities and processes. In addition to the expected predominance of silica-containing mineral dusts, various other components were identified, including fractions rich in lead, soluble salts, Zinc and Calcium. The possible sources of these components are discussed. The quartz fraction of the dust is calculated using a correction factor based on the composition of sericite (muscovite) and the measured concentrations of alumina and potash. The results are evaluated in terms of implications for the proposed use of a gravimetric methodfor industrial hygiene monitoring in underground mines. * Permanent address: Istitno Nazionale di Fisica Nucleare, Genova, Italy. Journal ofthe Mine Ventilation Society ofSouth Africa, January, 1988 1 Composition and size of dust in a Gold Mine atmosphere 1. INTRODUCTION Over past decades investigations of airborne dust on South African gold mines have focused largely on concentrations of siliceous mineral components. The present paper deals with part of a series of measurements designed to characterize the air borne dust, or aerosol, on a much broader basis, looking at both the major and minor components. By understanding the source materials, dust-gener ating processes, transport and dust sinks, we hope to arrive at a point where monitoring and control of dust will be placed on a sound technical basis. A particularly compelling need for this more fun damental understanding of all components of dust, as opposed to only the respirable quartz fraction, are the current evaluations of gravimetric sampling to replace the konimeter as the certified method for dust sampling. Results presented here are from preliminary sam pling in a Free State gold mine, where dust sam ples near specific dust-generating processes, e.g. drilling were collected. Such source samples were needed also to assist in the interpretation of dust samples collected with a streaker sampler in a re turn airway. These return-airway samples consti tuted an integration of multiple processes taking place in the mine (i). The results are preliminary in the sense that only single samples were collected at each site. This work is thus neither a comprehen sive survey of the mine, nor necessarily represen tative of general conditions. Nevertheless, the re sults do illuminate some of the mine sources of airborne dust. Some of these processes were ob vious. Others were unexpected and do not appear to have been reported in the published literature. 2. EXPERIMENTAL 2.1 Sampling Instruments Sampling was carried out with Stacked Filter Units (SFUs), a two-stage (dichotomous) sampler <2). The device consists of two Nuclepore polycarbonate membrane filters connected in series (Figure 1). Nuclepore filter membranes are characterized by an extremely uniform pore size, with pore axes aligned vertically to the membrane surface. This results in a comparatively sharp cut-off curve for particle size retention. Such a curve is shown in Figure 2 for an 8-|im pore diameter membrane, at 0,05 m/s face velocity. The first filter, which acted as a coarse, dispersion-particle sieve, was chosen to have 8-|im pore diameter, with effec tive 50 percent cut-off point diameter of 3,0-pm aerodynamic diameter. The second filter was a 0.4-pm pore diameter membrane, with an es sentially 100 percent retention efficiency for all particle sizes. Stacked Filter Units were connected to sampling trains consisting of a ballast bottle, a Gast DOA320A pump, powered by a 12-V, 40 A-h lead-acid battery, a 1-10 t/min flowmeter and a dry gasmeter. Each assembly, including battery, was packed in a steel carrying-case, and could be transported (with difficulty) by one man. Sampling times ranged between 20 minutes and one hour. 2.2. Sampling Strategy The intended sampling strategy was to follow the path of airflow through a section of a mine, sam pling in the vicinity of, or upstream and down- Figure 1. Components of the Stacked Filter Unit dichotomous aerosol sampler 2 Journal ofthe Mine Ventilation Society ofSouth Africa, January, 1988 Composition and size of dust in a Gold Mine atmosphere From PIXE the elemental concentrations are de rived. By means of standard X-ray fluorescence analysis procedures used in mineralogy, elemental concentrations were converted to standard oxide forms, with the exceptions of Cl. As chlorides in the mine atmosphere are derived from soluble salts, rather than from mineral oxides, it was con verted to NaCl. As Na was not measured quantita tively, this approximation accounts also for the Na mass. Sulphur in the airborne particles may have been derived from reduced forms (FeS), or in the oxidized state, as conversion sulphate (S04). It was calculated as the latter. Figure 2. Aerosol collection efficiencies for 0.4 and 8.0 \xm pore diameter Nuclepore membrane filters. X axis scale is in units of particle aerodynamic diameter. Particle deposition in the human nasopharynx region is super imposed. The 8.0 [xm filter 50% cutpoint occurs at the minimum in the natural bimodal aerosol mass distribu tion stream of localities or processes generating dust. Limitations of time and resources prevented com plete sampling at all identified processes. Sites sampled are described with the results in Section 3. In several instances physical layout of the mine and ventilation systems prevented upstream sam pling. A particular feature of the section of mine sam pled was that industrial-grade water used for dust suppression was drawn from the brackish local ground water. This brackish water is typical of the region and is used extensively as industrial-grade water by the mines. 2.3 Analysis Particle-induced X-ray Emission (PIXE) can be used to determine concentrations of elements A1 and heavier with minimum detection limits of a few nanograms per cubic metre. The following ele ments were routinely observed in mine-dust sam ples: Al, Si, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Cu, Zn and Pb, with integrated beam currents of 0,5 pC and irradiation times of approximately 2 minutes. Na was on occasion observed in the X-ray spectra at high concentrations (>300 ng/m3), but peak-fit ting and absorption-corrections made its absolute determination difficult. Analyses of SFU samples were performed using 4,5 MeV protons at the Crocker Nuclear Laboratory01. Streaker samples were analysed at the Schonland Research Centre with 3 MeV protons, with other parameters similar to those in the SFU analyses. 2.4. Composition Profiles Composition profiles or `fingerprints' are used as the major interpretive technique in this paper. The calculated oxide or compound concentrations were then summed for each sample stage, coarse or fine, and the percentage concentration of each component was calculated. The histogram of these fractional concentrations constitutes the profile. Comparison of ratios of concentrations of pairs of elements in the dust with the corresponding ratios from source materials provided further useful in formation. Sampled processes (or areas encompassing a num ber of processes) were examined from three as pects: (i) Profiles were constructed from the differences between upstream and downstream samples. By such differencing the downstream sample was corrected for amounts present in the up stream air, thereby characterizing dust-gener ating or removal processes in the intervening zone. In the absence of an upstream sample, a downstream sample from a strong source was assumed to provide a good approximation for a source profile. (ii) Increases in absolute concentrations relative to those in the upstream air gave an indication of the source strength in the locality. (iii) Comparison of the ratio of elemental quanti ties in fine and coarse dust on the filters pro vided an indication of the size distribution of individual elemental components. For the sake of brevity in the discussion, concen trations of components on either the coarse or fine filters will be designated by subscripts C or F, re spectively, Hence SiF=70 percent refers to the fractional concentration of Si02 on the fine filter stage. Unless specified otherwise, all references are to oxide masses or mass fractions. 3. RESULTS AND DISCUSSION Results from five localities or processes where dust was generated have been selected for discussion. Selection was made partly on the intrinsic interest of the process itself and partly on the ability to characterize the dust composition in relation to the processes. The samples selected were from: (i) drilling in a blind development end; (ii) drilling and whitewashing in a haulage way; (iii) blasting; (iv) return air from the stopes; and Journal ofthe Mine Ventilation Society ofSouth Africa, January, 1988 3 Composition and size of dust in a Gold Mine atmosphere (v) air from disused workings. 3.1. Drilling in a Blind Development end (DDE) This sample, code DDE, was taken 15 m from the face of a blind development end of a 4 m diameter haulage way. Five pneumatic drills were operating intermittently during sampling. Forced ventilation ducts conveyed air to within 5 m of the face. The sampler was positioned sufficiently far away from the face so that the coarser water droplets would settle and to allow some degree of mixing of intake air and dust and vapours generated at the face. The incoming air was not sampled at this site. muscovite. On the fine filter, alumina, surpris ingly, was below the detection limit. When potash was used as a tracer, silica in the form of musco vite accounted for 4 percent of the mass and silica in the quartz for 55 percent. Ratios of fine to coarse concentrations are presented in Table 1. The fine, inhalable, mineral fraction consituted only 4 percent of the coarse fraction at this site. Table 1 RATIO OF FINE TO COARSE CONCENTRA TIONS IN AIRBORNE DUST SAMPLES AT VARIOUS LOCALITIES The composition profile, shown in Figure 3, is dominated by the mineral components, comprising the oxides of Si, Al, K and Fe. On the assumption that all the ancillary silicate minerals are in the form of muscovite (sericite)(4) with composition Fl2.K.Al3. (Si04)3=2H20. K20.3A1203.6Si02(5) the fraction of silica (Si02) present in the form of mus covite was estimated. This was done twice, once using alumina (A1203) as the tracer and once using potash (K20). If all the alumina and potash in the K I 0Z p m0o 200 7 / / 7 / / /L/j l Code Locality ai2o3 Si02 so4 NaCl k2o CaO Ti02 Cr203 MnO Fe203 CuO ZnO PbO DDE Drilling develop ment -- 0,04 0,48 0,17 0,04 0,19 -- -- -- 0,06 -- 0,02 -- DMH Drilling main haulage -- -- 0,32 0,05 0,05 0,05 -- -- 0,08 -- 0,48 -- BLST Filtered blasting fumes RAS-1 Return air from stopes MRB Reftige Bay (Disused workings) 0,15 0,40 0,64 0,33 0,37 0,45 -- 2,42 1,97 4,90 -- -- 2,51 0,55 0,38 1,02 0,41 0,25 -- ------ ------ 0,44 0,48 1,16 -- 0,03 0,43 0,40 -- 3,13 -- 1,17 The Sodium and Chloride 1 s / f. / 71 1 t / !_ / /X// ^ n^-jT'l E/jr-q----J ______(t (TjsXl . ^ rr-- /z A1203 Si02 S04 NaCl K20 CaO Ti02 Cr203 MnO Fe203 CuO ZnO PbO elements which were observed in the underground dust came [771 FINE STAGE COARSE STAGE from the brackish service Figure 3. Dust composition profile from drilling in a blind development end, 5 drills operating, 15 m from the face. Sample code DDE. dust is due to muscovite only, the two calculations should yield a similar result. The remaining silica is then attributed to pure quartz mineral (Si02). For the coarse filter, silica in all forms accounted for 72 percent of the total mass. On the basis of alumina and potash contents, silica in the form of muscovite accounted for 16 percent and 5 percent respectively of the coarse stage mass. The balances of 56 percent and 67 percent, respectively, were assumed to be in the form of quartz. The dis agreement between the two values may indicate that, in this sample, the ancillary silicate minerals are richer in alumina than was assumed for pure water Next, in order of decreasing concentration in the profile, were the soluble ions Cl, Na and S04. In a previous report the presented evidence showed that the elements Cl and Na, and a portion of S concentrations observed in underground dust, arose from brackish ground water which is used as industrial-grade water and which is aerosolized by pneumatic drills and dust suppression sprays. Cal cium hypo-chlorite, Ca(OCl)2 is added to the water as a disinfectant. The amount of Cl from this source is likely to be small compared with that in the natural components, as can be seen from the amount of dissolved solids in the fissure water (Table 2, Sample D). The presence of these ele ments in these samples is further confirmation of this observation. Table 2 shows the concentrations of soluble ions in water collected at various points in the mine. 4 Journal ofthe Mine Ventilation Society ofSouth Africa, January, 1988 Composition and size of dust in a Gold Mine atmosphere Sample C was taken from an industrial-water pipe in the development end during the dust-sam pling interval. Chloride, sodium, sulphate and cal cium were the dominant ions in the water, in that order. The fractions of sodium chloride in the air borne dust collected on the course and fine filter was 5,9 percent and 19,7 percent respectively. These values were lower than expected from pre vious measurements'6* especially since a visible cloud of spray was present during the sampling. The higher value of NaCl in the fine fraction indi cates that the size distribution of salty droplets has a maximum at a smaller diameter than the mineral particles (see Table 1). In this case, since the sam pling was close to the source, the droplets had not had sufficient time (15 to 30 s at approx. 1 m/s air speed) for significant evaporation to occur which would lead to a smaller particles. This may indi cate that many of the water droplets were gener ated in the sub-3 pm aerodynamic diameter size range. Table 2 DISSOLVED SOLIDS CONTENT (mg/) OF INDUSTRIAL-GRADE AND FISSURE WATER FROM A FREE STATE GOLD MINE Sample No. Site pH Total dissolved solids Calcium, Ca Magnesium, Mg Sodium, Na Potassium, K Bicarbonate, HC03 Chloride, Cl Sulphate, S04 Iron, Fe Manganese, Mn Copper, Cu Zinc, Zn A Drill Feed Water B Industrial Water Dam C Drill Feed Water, Develop ment End D Fissure Water 6,25 4576 374 28,5 1150 29,1 24,4 1660 1055 0,04 0,99 0,02 0,64 6,05 4650 419 28,8 1160 29,0 31,7 1675 1460 0,04 1,00 0,02 0,40 5,9 5050 400 26,6 1280 25,2 24,4 2090 900 0,01 1,40 0,01 0,50 7,1 4610 375 12,5 1300 10,5 51,2 2190 465 0,02 0,07 <0,01 0,03 Table 3 RELATIVE COMPOSITION OF SOLUBLE SALTS IN INDUSTRIAL QUALITY WATER; COARSE AND FINE DUST AT A BLIND DEVELOPMENT END (SAMPLE CODE DDE) Component Water, sample D Dust, coarse Dust, fine so4 NaCl Ca 1,00 3,74 0,44 1,00 4,54 0,66 2,82 4,54 0,73 Zinc concentrations had time variations different from the other element... The lubricating oil is a possible source The zinc oxide coarse and fine fractional concen trations at this site are 1,9 percent and 0,8 percent respectively, which were among the highest values measured. Zn concentrations had time variations very different from those of many of the other ele ments measured'1'7'8*, peaking during the drilling shift. This would appear to eliminate both the reef and water as major sources of this element, since both of these show peak concentrations during blasting. Furthermore, although Zn concentrations in the industrial water are increased by a factor of 20 relative to that in fissure water (Table 2), the water concentration of Zn would still be two or ders of magnitude too low to account for the ob served levels in dust, when Cl is used as a tracer for water-derived components. The Zn content of lubricating oil in the pneumatic drills is one poss ible source, which seems to be confirmed by the high fractional concentrations in this sample which was taken close to operating drills. This possibility remains to be investigated. The ratios of S04, NaCl and Ca in the water and in the coarse and fine sample fractions are given in Table 3. The relative compositions of the three components in the coarse dust is seen to be similar to that in the water. On the fine filter, however, S04 is enriched by a factor of 2,8 relative to NaCl and Ca. The excess S04, after the amount attri butable to the industrial water contribution has been substracted, amounts to 8 percent of the fine mass. This excess sulphur could be derived from pyrite (FeS), an ancillary mineral which forms 3 percent of typical reef(4). If all the fine Fe were in the form of pyrite (as opposed to Fe203) it would account for only a further 3 percent of the mass attributed to S04, leaving a balance of 5 percent. As high (S04)F fractions also occur in the intake air to this section of the mine (S04 F = 18 percent) the most likely source of excess fine S04 is sulphate derived from S02 in the surface atmosphere, and carried into the mine with the intake air. 3.2. Drilling and Whitewashing in a Main Haulageway (DMH) Several operations were being conducted in this locality: intermittent drilling of the hangingwall; attachment of galvanized steel-mesh bratticing; and spraying of the hangingwall with a coarse slurry of slaked lime (Ca(OH)2). Air movement through this zone was slow (1 m/s) which allowed accumulation of relatively high dust concentra tions. Simultaneous upstream and downstream samples were collected over 30-minute intervals. Composition profiles, code DMH, for coarse and fine fractions corrected for dust in the upstream air, are presented in Figure 4. Two major compo nents are present: first, mineral dust, from drilling into the hangingwall, which is present in the coarse profile only. The absolute mineral concentration Journal ofthe Mine Ventilation Society ofSouth Africa, January, 1988 5 Composition and size of dust in a Gold Mine atmosphere 60 K 02 50 5o c20u HQ 1 20 6 Sb A1203 Si02 S04 NaCl K20 CaO Ti02 Cr203 MnO Fe203 CuO ZnO PbO Table 4 RATIOS OF DOWNSTREAM TO UPSTREAM CONCENTRATIONS OF DUST COMPONENTS AT A LOCALITY IN A MAIN HAULAGEWAY WHERE ROCK DRILLING AND WHITEWASHING OF THE HANGINGWALL WERE OCCURING (CODE DMH) Oxide A1A Si02 Composition Fine fraction Coarse fraction # 7,3 0,97 6,8 so4 NaCl k2o 1,6 2,9 1,3 2,7 2,0 7,4 CaO Fe203 ZnO 4,0 1,4 23,4 5,8 * 4,8 # Downstream A1 below detection limit. Ratio = 0,0 * Upstream Zn below detection limit. Ratio not defined. Figure 4(a). Composition profile obtained by subtracting up from down-stream dust concentrations in a haulage way where drilling, and white washing were taking place. Coarse stage 50 K 45 20 40 0w 35 a. 0S0 30 wQ 25 20 < 15 20 10 6 5 0 A1203 Si02 S04 NaCl K20 CaO Ti02 Cr203 MnO Fe203 CuO ZnO PbO (77 PINE STAGE Figure 4(b). As above, fine stage increased sevenfold in the coarse stage (Table 4), while in the fine stage it decreased slightly, indicat ing that the sampled locality was a net sink of fine mineral dust. The composition of the coarse frac tion in the DMH sample, Si:Al:K=28:5:l, was close to the mineral composition of dust in the up stream air, Si;Al:K=28:5:l. Of the 65 percent silica in the coarse stage, 21 percent and 27 per cent were present in the form of muscovite, calcu lated on the alumina and potash contents, respecti vely. The agreement between these results is better than that for samples taken at the previous locality. The fraction of silica as quartz was there fore between 38 percent and 44 percent. 6 Secondly the measured CaO components in the coarse and fine fractions were 27 percent and 46 percent respectively. This represented a substantial twenty three fold increase iri'the coarse and a four fold increase in the fine CaO concentrations com pared with the intake air (Table 4). Spraying of the hangingwall with slaked lime was the obvious source of this CaO. As was to be expected, the low-pressure spraying of a concentrated slurry pro duced predominantly coarse particles. Associated with the fine Ca was a substantial amount of S04 ((S04)F = 27 percent). Since this profile has been corrected again for the upstream air excess (S04)F cannot be attributed to the intake air since (S04)F is 2,5 fold greater than NaClF; sources of (S04)F additional to the grade water are required. It is not apparent why, if the two elements were indeed both from the slaked lime slurry, S04 and Ca should fractionate differently between coarse and fine particles. Electron microscope examination of mine aerosol particles, showed Ca to be associated with S in evaporated crystals, sometimes abutting chloride salt crystals but often also as pure Ca-S crystals'6'. The extent to which S04 is generated from industrial-grade water, slaked lime, pyrite and other possible sources remains to be deter mined. Three minor components warrant brief mention. Increases in the Cl content, indicative of the effect of the spray water, were moderate at three fold and two fold for the coarse and fine stages, re spectively, compared with a seven fold increase of Cl in the coarse mineral dust (Table 4). Additional spray points or more rapid settling of mineral com ponents relative to that of the salt components may account for the higher concentrations of NaCl in slightly aged aerosols, that is, several minutes downstream of the drilling operations. The absence of other mineral components from the fine dust profile rules out the likelikhood that FeS2 is the source of the observed (Fe203)F = 10 percent, which may have been derived from abra sion of steel drill bits. However, the presence, in the coarse dust, of Mn and Cr together with an iron component (4 percent), in the ratio Fe:Mn:Cr = 36:3:2, is more indicative of hardened tool steel as the source. Journal ofthe Mine Ventilation Society ofSouth Africa, January, 1988 Composition and size of dust in a Gold Mine atmosphere The absolute amount of Zn in the coarse fraction (640 ng/m3) exceeded that in the fine fraction by a factor of two. However, the large coarse-fraction mineral component reduced the fractional concen tration of Znc to 0,2 percent, compared with ZnF = 3,0 percent. The increase in Zn between up stream and downstream was fivefold in the coase fraction, while no Zn was present in the upstream fine fraction (Table 5). The lack of correlation be tween increases in CaO and ZnO in the coarse and fine fractions appears to rule out a common source. If Zn were derived from the galvanized steel mesh, one would expect mechanical dispers ion, for example abrasion, to produce Zn-particles in the coarse fraction. Pneumatic drills are a com mon factor between this and the previous locality, each of which had high ZnO concentrations. As mentioned above, lubricating oils used in the drills were a possible source of airborne zinc. 1 l 1 E11 i7 1 1ki/ -1Z 1/ pj, 1/ [l/p..-1/fA] ,-pA1203 Si02 S04 NaCI K20 CaO iit_, t _ | --^ | /I/p ,--,----n- Ti02 Cr203 MnO Fe203 CuO ZnO PbO 1Z71 FINE STAGE ^55 COARSE STAGE 3.3. Blasting (BLST) Air samples were taken downstream of a horizon tal tunnel which was being developed on a twoblast-per-day cycle. Air and blasting fumes from this development end were extracted through a se ries of filters, comprising a water-spray bank, a KMn04-impregnated vermiculite filter bed and bag filters. The sampler was located downstream of the bag filters after which it was ducted to an upcast exhaust shaft. Sampling started 10 minutes before the blast and continued for 40 minutes afterwards. The profiles of sample code BLST are shown in Figure 5. Two important noteworthy features of this profile are: (i) the high Pb concentrations, especially in the fine stage, for which PbF = 33 percent exceeds SiF = 25 percent; and (ii) correspondingly high K fractions, KCF = 18 percent and 6 percent, respectively. The ratios (Si:Al:K)F = 2,1 : 0,17 : 1,0 indicate a composition markedly different from that of other samples of mineral dust containing these three ele ments or from the composition of sericite. A considerable enrichment in the fine K fraction had occurred. Since this was not associated with any other mineral elements, another source must be identified. The presence of KMn04 in the vermiculite filter bed is an obvious possibility, even though the Mn concentration did not increase sig nificantly, this may be discarded by examing the evidence from streaker sampling results on a neighbouring mine. The streaker sampling encom passed blasts which occurred as part of regular mining operations, with air being exhausted along airways without passing through KMn04-impregnated vermiculite beds, or any other filters. In these samples the K concentrations were increased considerably. As these K levels which were high relative to other mineral components, notably Si and Al, did not occur during drilling or clearing of the same ore bodies, it must be concluded that the K is aerosolized during the blast. Figure 5. Composition profile of filtered blast fumes The materials present during the blast are the ex plosives, detonator caps, safety fuse, igniter cord and the ore. The temperatures reached during the blast (up to 5000 C) are such as to vaporize the oxides formed as part of the explosion, as well as the casing of the explosives and caps. In addition, in the area immediately surrounding the explosive, chemical as well as physical effects may occur, in which case K components of the ancillary minerals (sericite) may be liberated selectively into the va pour phase. Further investigations are needed to elucidate these high K concentrations. 3.4. Return Air From Stopes (RAS-1, RAS-2) Two samples are considered under this heading, both collected towards the end of the drilling shift (13h00). The first sample, RAS-1 was taken at the top of an inclined shaft equipped with a chair lift. The air velocity from the lower stoping was over 3 m/s which resulted in the transit time of the air between the drilling site and the sampling point being several minutes. Furthermore, since sam pling took place towards the end of the shift, most drilling would have been completed. The second sample, RAS-2, was taken closer to the working faces, where the air from a stope entered the re turn airway. Composition profiles for the two samples are pres ented in Figures 6 and 7. Mineral components dominate. The ratios of the mineral elements for the two samples are (Si:Al:K)F = 17:4:1 and 34:0:15,3 and (Si:Al:K)c = 26:5:1 and 32:6:1. The quartz components, calculated from total silica corrected for alumina and potash contents, are shown in Table 5. Agreement between pairs of quartz values is, in each case, better than 15 per cent. This agreement renders the reasonable as sumption that the auxilliary minerals have the same composition as muscovite. Journal ofthe Mine Ventilation Society ofSouth Africa, January, 1988 7 Composition and size of dust in a Gold Mine atmosphere N 1 Z0 h 0C, y UQ 1 Table 5 QUARTZ COMPONENT OF DUST IN RE TURN AIR FROM STOPES, CALCULATED FROM ALUMINA AND POTASH CONTENTS OF DUST, BASED ON MUSCOVITE (SERICITE) COMPOSI TION* Sample code Fine Stage Coarse Stage Total Quartz Si02 Total Quartz Si02 Measured Calculated from Measured Calculated from sio2 ai2o3 k2o Si02 ai2o3 K20 ~7~ / i ! es 1 * 8) l / /S 3 1 -----p3>------- p-n a--j-------- ____ | 7 jXM------- pS A1203 Si02 S04 NaCl K20 C0 Ti02 Cr203 MnO Fe203 CuO ZnO PbO 1771 FINE STAGE kWM COABSE STAGE Figure 6. Composition profile of dust in return airfrom stopes. Sample code RAS-1. RAS-1 RAS-2 MRB 47 36 37 52 73 # 66 62 39 28 33 38 * Muscovite composition: Si02: AhOjiKoO -- 3,83 : 3,26 : 1,00 # A1 below detenction limit. 41 45 50 55 31 30 latter case, a predominantly fine rather than only a coarse Pb component would have been expected. The absolute concentration of Pb02 was 1,4 pg/m3, a value typical of daytime values in the at mosphere in the centre of Johannesburg or other major cities. This level is thus within values cur rently tolerated for environmental health pur poses. 771 FINE STAGE COAKSE STAGE Figure 7. Composition profile of dust in return air from stopes, as air first rejoins a haulage way. Sample code RAS-2. Figure 8. Composition profile of dust in airflow ing from a section of disused workings sealed off from the main ventilation system. Sample code MRB. The Fe and S04 components were the next most abundant in the return air. The Fe fraction is somewhat higher than in previous samples. The sources of these components would be similar to those discussed above. In sample RAS-1 the Zn fractions of the course and fire samples 0,9; 1,0 percent respectively which were relatively large. Zn was entirely absent from sample RAS-2. The only other feature of note was a small Pbc fraction of 1,8 percent in RAS-1. This may be due either to Pb, from a previous blasting cycle, resuspended as a coating on coarse mineral dust, or to a blast that had been set off before the scheduled time. In the 3.5. Air From Disused Workings (MAN-REFUGE BAY) (MRB) This man-refuge bay was a blocked-off length of tunnel, 20 m long, leading off a haulageway. The dead-end of the bay was sealed off from disused workings by a concrete wall; A perceptible current of warm air entered the refuge bay through a 150 mm diameter opening in the wall. The sampler was located close to this inlet. This sample, code MRB, was considered to be representative of the air in the disused workings, after it had passed through with an unknown residence time. 8 Journal ofthe Mine Ventilation Society ofSouth Africa, January, 1988 Composition and size of dust in a Gold Mine atmosphere The concentration profiles from the refuge bay are shown in Figure 8. Striking features are relatively low mineral concentrations of SiCF = 38 percent; 39 percent respectively and high fine sulphate; S04 = 26 percent. If air moved slowly through the dis used workings then it would be expected that the coarser particles would settle out. This would lead to a larger ratio of fine to coarse particles, which is, in fact, observed. Table 1 shows that these fineto-coarse ratios for the mineral components were ten times higher than for samples close to the dril ling in the development end. The proportion of sil ica present as quartz is shown in Table 5. This sample had a 4,1 percent Pb component. The presence of Pb in this sample taken approximately 20 hours after the previous blast, indicates that blasting fumes penetrated into the disused work ings and were being flushed out with a consider ably longer time constant (minimum 20 hours) than the average ventilation air. The ratio PbF:Pbc The presence of lead in the ventilation air indicated that blasting fumes penetrated into the Spraying to suppress dust produced a secondary aerosol of chloride and calcium sulphate salts, de rived from dissolved solids in the water. High con centrations of coarse calcium-rich particles were identified during the spraying, of hangingwalls with slaked lime. Zn-rich particles were associated with pneumatic drilling. However, the exact source of the zinc has not been positively identified. A por tion of fine sulphate can be attributed to second ary-conversion sulphate, present in the surface air and drawn into the mine by the ventilation system. The presence of these various secondary aerosol components has a significant bearing on current in vestigations into the suitability of gravimetric sam pling for industrial hygiene monitoring in under ground mines in South Africa. Proposals presently being considered, include the use of a cyclone pre separator, and allowing a filter to collect the respi rable fraction below some defined cut-off point. If one assumes that quartz is still the major hazard ous component in underground dust and if compli ance with standards and compensation levies are The silica content of dust is highly variable from 25% to 70% discused workings = 1,17 is close to the BLAST ratio which indicates that some of the fine Pb is primary blast fume, as opposed to Pb on resuspended coarse mineral dust. Absolute concentrations of (Pb02)CF = 680 and 800 ug/m*3 1re2spectively were again within common urban environmental levels and not a matter for immediate concern. Copper at this site, Cuc = 10 percent, was the highest Cu fraction measured. Underground equipment which could have released Cu aerosol included electric motors and switchgear contacts (minor) and brazing of copper or bronze with gas or electric arcs. The specific source of Cu in this sample was not obvious. Clearly it was not asso ciated with blasting. 4. CONCLUSIONS Composition profiles demonstrate that aerosols, while dominated by silica mineral components in almost all cases, showed considerable variation in different localities of the mine. Major secondary components have been identified. This is believed to be the first time that some of them have been reported in the open literature. Specifically, high lead and Potasium particle concentrations were measured and associated with blasting. Residual amount of lead observed with the exception of those in the exhaust blast fumes, were not at con centrations that would give rise for concern. Stan dard practice for ventilation of mines for the ex haust of noxious gases appears to be adequate for removing Pb fumes as well. to be based on the proposed gravimetric stan dards, then the present results show that such an approach could lead to several anomalies: (1) The silica content of the dust is highly vari able, from 25 percent to 70 percent of the fine fraction. Part of the fine respirable particles were sulphates brought in with the intake air, which can constitute up to 30 percent of the mass for par ticles with an aerodynamic diameter less than 3 jam. The sulphate content of the intake air is highly variable and the inclusion of sulphate in a measurement of air quality underground (by gravi metric sampling) would introduce an arbitrary and significant variable. (2) Regional differences, both within and be tween mines, in the dissolved solids content of water, will lead to large differences in the salt con tent of the aerosol. The anomalous situation may arise whereby the more extensive the use of dust suppression sprays, the higher the gravimetric con centration of dust might be. While quality and source of water are within the control of mines, the situation as sketched does not lead to a sound base for air quality measurements. Clearly, desirable characteristics of a monitoring technique are that it should be sensitive and yield a direct measurement by a rapid and inexpensive method. Gravimetric determinations satisfy these three criteria but give only an indirect measure ment of the desired quantity, quartz. The argu ment above attempts to show that the gravimetric method is in fact so poorly correlated with quartz content as to be inappropriate. X-ray diffraction has the virtue of providing a direct measure of Journal ofthe Mine Ventilation Society ofSouth Africa, January, 1988 9 Composition and size of dust in a Gold Mine atmosphere quartz. It was, however, until recently, not sensi tive enough for routine analysis of the small sam ple masses obtainable by personal-type samples. (Recent improvements in X-ray diffraction instru mentation have made it possible to obtain diffrac tion measurements, within a few minutes, of the quartz content of personal filter samples of mine dust, collected over the time of a single shift(9). In this work it has been shown that the measure ment of the elemental concentrations in dust sam ples by energy dispersive X-ray analysis (PIXE) may be used to calculate the portion of silica pres ent as quartz. While considerable further work is required to validate an approach for use in indus trial hygiene monitoring, the feasibility has been established of using an assumed composition of secondary silicate minerals (muscovite) to calculate the quartz component of the silica. PIXE measure ments are also rapid and sensitive. Preliminary cal culations have shown that if PIXE is set up in a central specialized laboratory for the gold mining industry, similar to the present arrangement for konimeter sample analysis, the unit cost per sam ple analysis could be reduced to acceptable values. lifornia, Davis, while supported by a University of the Witwatersrand Council Overseas Fellowship, with further support from a CSIR-Foundation for Research Development comprehensive grant. The generous hospitality of Prof T.A. Cahill and staff of the Crocker Nuclear Laboratory is gratefully ac knowledged. Mr. J. Cruise is thanked for dis cussions regarding explosives in underground min ing, and for critical comments on the manuscript. 6. REFERENCES 1. ANNEGARN, H.J., ZUCCHIATTI, A. and SELLSCHOP, J.P.F. PIXE BOOTH-JONES P. characterization of airborne dust in the mining environment. Nucl. Instr. and Methods B (1987). Vol. B22 1987, pp 325-330. 2. CAHILL, T.A., ELDRED, R.A., BARONE, J. and ASHBAUGH, L. Ambient aerosol sampling with stacked filter units. Report No. FHWA-RD-78-178. (1978). 79 pp. US NTIS, Springfield, Virginia 22161. 3. CAHILL, T.A. (1975). In New uses for ion accelerators. Ed J. Ziegler, Plenum (New York), pp 1-72. 4. FEATHER, C.S. and KOEN, G.M. The mineralogy of the Wit watersrand reefs. Minerals Sci. Engng., 7, (1975), pp 189-224. 5. DANA, E.S. (1898). A textbook of mineralogy. 4th Ed. revised by W.E. Ford. John Wiley and Sons (New York). 6. ANNEGARN, H.J., STORMS, H., VAN GRIEKEN, R.E. and BOOTH-JONES, P.A. Composition and size of individual particles from a gold mine atmosphere. Mining Science and Tech. (1987). Min ing Science & Tech. Vol 5 1987, pp 111-119. 5.5 ACKNOWDLEDGEMENTS The authors acknowledge with thanks the gener ous financial and logistical support of Rand Mines Ltd. Thanks are due to the assistance provided by the mine personnel during the sampling expedi tion. Dr. Annegan performed part of this work at the Crocker Nuclear Laboratory, University of Ca 7. ANNEGARN, H.J. Time series analysis of PIXE aerosol measure ments. Nucl. Instr. and Methods B (1987). Vol B22 1987, pp 270-274. 8. ANNEGARN, H.J. SUCCHIATTI, A., SELLSCHOP, J.P.F. and BOOTH-JONES, P.A. Time variations of dust concentration and elemental composition in a gold mine. Proc. Mine Ventilation Society of SA. Symposium on airborne pollutants: their effects, measurement and control. 25-26 March 1987, Vereeniging. 9. GARDINER, L. Chamber of Mines of South Africa Research Orga nization, personal communication. NEW CERTIFICATE FOR MEMBERS Recently there has been numerous re quests from members for new certificates to be printed, in which our coat of arm is incorporated. These certificates have been produced and are available to all fellows. In order to cover the cost of having names of fellow written on the new cer tificates and postage, R6,00 per certificate will be charged. All fellows who would like a new certificate should contact: Mine Ventilation Society Kelvin House 2 Hollard Street Johannesburg Tel. No. 832-2177 (morning only) 10 TOE NINE VENTILATION SOCIETY OF SOUTH AFRICA This is to Certify that has this day been admitted as a Fellow of the Mine Ventilation Society of South Africa Given under the Seal of the Society President Dale J| j j1 Journal ofthe Mine Ventilation Society ofSouth Africa, January, 1988