Ore Processing by PGM Concentration Process and Assessment of CO 2 Equivalent Emissions and Environmental Damage Directly Involved Junior Mabiza-ma-Mabiza and Charles Mbohwa Abstract Platinum group metals are more and more pointed out as key players to contribute to addressing the making headway issues of environmental damage impacts through technological innovations. Of immediate past, interest in hydrogen has grown rapidly resulting to the development of the concept of hydrogen econ- omy to address two growingly noticed challenges namely climate change impacts due to GHG emissions and the need for clean energy, security and sustainability supply. The recognitions to PGM are of without a doubt, but goings-on around PGM recovery process are reported with environmental concerns; the best known are identified as land transformation, livestock and wildlife affected by use of chemicals and other non-renewable resources. Life cycle assessment analysis of ore-concentration was developed and equivalent carbon dioxide emissions quanti- fied. One tonne of Ore-based PGM Concentrates, a total amount of equivalent carbon dioxide of about 1.574,96 kg CO 2 -eq was associated with this process. In an annual initiative, the concentrator can process up to 36,547 million metric tons of ore milled accounting for 57.5 million kg CO 2 -eq. Important emissions in this phase are waterborne and emissions to soil. Keywords Bushveld complex Á Direct environmental damages Á Equivalent car- bon dioxide emissions Á Life cycle inventory assessment Á Ore-based platinum metals concentration process Á Platinum group metals J. Mabiza-ma-Mabiza (&) Faculty of Engineering and the Built Environment, Department of Quality and Operations Management, University of Johannesburg, C Green 6, Bunting Road Campus, Auckland Park, Johannesburg, Gauteng Province 2092, South Africa e-mail: [email protected]; [email protected] C. Mbohwa Faculty of Engineering and the Built Environment, University of Johannesburg, C Green 5, Bunting Road Campus, Auckland Park, Johannesburg, Gauteng Province 2092, South Africa e-mail: [email protected] © Springer Science+Business Media Singapore 2016 S.-I. Ao et al. (eds.), Transactions on Engineering Technologies, DOI 10.1007/978-981-10-1088-0_21 273 [email protected]
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Ore Processing by PGM ConcentrationProcess and Assessment of CO2 EquivalentEmissions and Environmental DamageDirectly Involved
Junior Mabiza-ma-Mabiza and Charles Mbohwa
Abstract Platinum group metals are more and more pointed out as key players tocontribute to addressing the making headway issues of environmental damageimpacts through technological innovations. Of immediate past, interest in hydrogenhas grown rapidly resulting to the development of the concept of hydrogen econ-omy to address two growingly noticed challenges namely climate change impactsdue to GHG emissions and the need for clean energy, security and sustainabilitysupply. The recognitions to PGM are of without a doubt, but goings-on aroundPGM recovery process are reported with environmental concerns; the best knownare identified as land transformation, livestock and wildlife affected by use ofchemicals and other non-renewable resources. Life cycle assessment analysis ofore-concentration was developed and equivalent carbon dioxide emissions quanti-fied. One tonne of Ore-based PGM Concentrates, a total amount of equivalentcarbon dioxide of about 1.574,96 kg CO2-eq was associated with this process. In anannual initiative, the concentrator can process up to 36,547 million metric tons ofore milled accounting for 57.5 million kg CO2-eq. Important emissions in thisphase are waterborne and emissions to soil.
Keywords Bushveld complex � Direct environmental damages � Equivalent car-bon dioxide emissions � Life cycle inventory assessment � Ore-based platinummetals concentration process � Platinum group metals
J. Mabiza-ma-Mabiza (&)Faculty of Engineering and the Built Environment, Department of Qualityand Operations Management, University of Johannesburg, C Green 6,Bunting Road Campus, Auckland Park, Johannesburg, Gauteng Province 2092,South Africae-mail: [email protected]; [email protected]
C. MbohwaFaculty of Engineering and the Built Environment, University of Johannesburg,C Green 5, Bunting Road Campus, Auckland Park, Johannesburg,Gauteng Province 2092, South Africae-mail: [email protected]
© Springer Science+Business Media Singapore 2016S.-I. Ao et al. (eds.), Transactions on Engineering Technologies,DOI 10.1007/978-981-10-1088-0_21
273
1 Introduction
Energy is the life force driving our modern civilization and its dimensions, beingeconomy and development, work, spare time, social and physical welfare all isinfluenced by the supply of a sufficient and uninterrupted energy. However thechallenge of the demand for energy worldwide has been growing at significant rateand of recent clean energy supply is a new restriction.
Of immediate past, interest in hydrogen has grown rapidly resulting to thedevelopment of the concept of hydrogen economy. The primary reason for thisawakening is that hydrogen economy may be an answer to two major challengesalready faced by the world, which are growingly noticed nowadays. The firstchallenge is a severe series of environmental impacts resulting to climate changewhich is caused by greenhouse gas emissions (GGEs) formed by carbon dioxide(CO2) and equivalent carbon dioxide (CO2-eq) emissions. CO2-eq emissions beingother pollutants such as NOx, SFx, and SOx; they result both with CO2 emissionsmainly by burning fossil fuels, coal and natural gas. The second challenge, not theleast, is the need for security of energy and sustainability supply.
Hydrogen economy may be a major key answer to strip off CO2 calamities andcontribute to sustain energy security supply. Hydrogen economy is defined as thefree CO2/CO2-eq emissions built-up system, in which one of the universal energycarriers is hydrogen, the other electricity. In hydrogen economy the two energycarriers will coexist with possibility to generate one another to provide, convey andstore energy [1].
Hydrogen satisfies to the requirements of an energy carrier which, in the longrun, might meet all energy needs together with electricity. Such energy systemwould be independent of energy sources since both electricity and hydrogen can beproduced from the most available primary energy sources and added to the energysupply mix [2].
Hydrogen produced from water by electrolysis process is the most environ-mentally friendly but with prerequisites to be met for efficient and effective activity.The process involves platinum group metals (PGM) as catalyst to increase theefficiency through the use of solid polymer electrolyzer (SPE) currently experi-mented as the best electrolyzer high output volume of hydrogen. However theengineering recovery process of PGM suffers criticisms as reported by manyscholars of real concerns of emissions to the immediate environment affecting localcommunities and seen as future threats to the regional biodiversity, contributing toclimate change globally as well.
South Africa is the largest world PGM economy accounting about 75 % of theglobal reserves. The country’s PGM’s wealth has been seen as a significant com-petitive advantage for the global HFCT development initiatives in view of theabundant platinum metals deposits in the country in terms alternative solutionsthrough clean and renewable energy supply, mitigation of GHG emissions, newtypes of business ventures, etc. [3].
274 J. Mabiza-ma-Mabiza and C. Mbohwa
The global supply of PGM (Table 1) is largely dominated by South Africa dueto its large economic reserves in the stratiform deposits built with Precambrianmafic to ultramafic layered intrusions known as the Bushveld Complex. SouthAfrican PGM reserves are estimated to be 71,000 tonnes whilst the global reservesare estimated to be 80,000 tonnes [4].
Dominant PGM producers are progressively raising a capital reserve of platinummetals for the global hydrogen fuel cell technology (HFCT) industry. According to[5], it is significant to recognize that resource issues such as ore grade declination,increase of more energy and water consumption and environmental issues arepossible constraints on future PGM production. The rate of PGM productiongrowth may also be constrained by demand which is foreseen. South Africa, forinstance, prepares to make reserves available to supply 25 % of the global catalystdemand for the HFCT industry by 2020 [6].
The South African miner, Anglo Platinum Limited is the largest producer ofplatinum group metals in the world. It owns varied mines and operates threesmelters of which Waterval (Rustenburg) where precious metals are refined andMortimer (Limpopo) both located on the western limb of the Bushveld complex.The third smelter, Polokwane (Polokwane), is located on the eastern limb of theBushveld complex (Fig. 1) [7]. The Bushveld Complex is the world’s largest PGMreserve that has led the global production of PGM since 1971. Bushveld Complexabounds also in Chromium and Vanadium with the world’s largest reserves [8].Due to the Bushveld Complex location in South Africa, the country covers thelargest potential economic of PGM resources ever discovered in the world, which isestimated about 80 % of the global reserves.
Operational sites of the Anglo American Platinum.Anglo American Platinum operates in the Western limbs of the Bushveld
Complex exploiting the world’s largest known igneous complex that extends over65,000 km2 and reaches a depth of about 7 km.
Table 1 PGMs reserves and production by country [4]
Country Production Reservesb Reserve baseb
t Pt t Pd t PGMs t PGMs t PGMs
South Africa 165.83 86.46 310.92 63,000 70,000
Russia 27.00 96.80 138.30 6200 6600
Canada 6.20 10.50 20.20 310 390
Zimbabwe 5.30 4.20 11.00 – –
United States 3.86 12.80 – 900 2000
Columbia 1.40 – – – –
Australia *0.90a *0.73a – – –
World 212 219 509 71,000 80,000aAssuming Australia is credited with PGMs extracted from ores and concentrates exported toJapanbThey are broadly similar to reserves and resources as used in South Africa, Canada, Australia, andelsewhere. With t = tonne metric, Pt = platinum, Pd = palladium
Ore Processing by PGM Concentration Process … 275
An average concentration of PGM of about five grams (5 g) can be found in onemetric ton (1000 kg) of mined ore which can be sent directly to the Precious MetalsRefinery (PMR) unit. The rest of the mined ore undergoes ore concentrationoperations. Precious metals are completely recovered from the mined ore [8].
2 Ore Concentration Unit
Ore mined is received at the ore concentration unit mainly for the separation ofvaluable contents to rocks and sand. Ores undergo crushing, milling, and wet-screening to obtain pumpable slurry bearing the precious metals. Separation occursin flotation cells where the reagents (chemicals) are added to aerate slugs carryinghigh-grade collected PGM [9].
Operations of ore concentration are accountable for large amounts of water usewith possibly large emissions to water and soil. An approximate composition of ametric ton received at the ore concentration unit of Waterval is given in Table 2.
Fig. 1 Location of Anglo Platinum operations in the Bushveld complex. Source [7] (color figureonline)
Table 2 Analysis of concentrates at the Waterval concentration unit [15]
Al2O3
(%)CaO(%)
Co(%)
Cr2O3
(%)Cu(%)
FeO(%)
MgO(%)
Ni(%)
S(%)
SiO2
(%)PGM(g/t)
Total(%)
Anglo-platWaterval
3.2 4.7 0.08 0.80 2.1 20 15 3.6 9 34 143 92
276 J. Mabiza-ma-Mabiza and C. Mbohwa
Ore ConcentrationUnits
Fig. 2 Operational sites ofthe Anglo American Platinum[14]
Ore Processing by PGM Concentration Process … 277
This is a typical composition of a layer of the western Bushveld complex pre-dominated with sulfur and iron [10].
Schematic Recovery Process of the PGM at Anglo American (Fig. 2).In general ore concentration process results in land transformation, livestock,
fauna, and flora affected by use of chemicals and other non-renewable resources.Important and varied wastes are generated which interact with local communities.Airborne emissions affect and put under stress local communities and the immediateenvironment such as underground water, livestock, fauna, and flora. In return,mining companies put in place appropriate management systems tailored to ISO14001:2004 standards to track legal compliance in an effort to prevent pollution [9].
3 Methods of Assessment and Instruments
Life-Cycle Assessment: Definition, Goal and Scope (ISO 14040)The life-cycle assessment, also known as ISO 14040, is a method in which rawmaterial and energy consumption, types of emissions and other major factorsrelated to a specific product are being measured and analyzed over the entireproduct life cycle from an environmental point of view [11].
Life Cycle Inventory Analysis (ISO 14041)The inventory analysis, for such specific products or techniques, consists ofdeveloping a process tree, also called flow-material chart, in which all processesfrom the raw materials extraction and input materials through operation, to finalproduct, waste recycle, disposal treatment, and emissions are mapped out andconnected, and mass and energy balances are closed [11]. The Life Cycle InventoryAnalysis (LCIA) of a single or a simple set of unit processes (Fig. 3) may beestablished using a simple input/output balance sheet analysis. In the case of a morecomplex LCIA processes however, LCIA analysis can be achieved through specificand appropriate LCA tools such as ‘Umberto for carbon footprint software pack-age’. Umberto for carbon footprint package is introduced in the followingsub-headings. Equivalent carbon dioxide can be quantified at the inventory analysisstage of LCA development.
Sketch of Input/output single stage or unit process in a flow chart.
Umberto for Carbon Footprint Software Package:Umberto is a helpful tool which is used by LCA professionals, scientists andmanufacturing companies. Umberto trademark comprises a number of productpackages which are specifically designated for different approaches in the LCAanalysis [12].
278 J. Mabiza-ma-Mabiza and C. Mbohwa
The concept of Equivalent Carbon Dioxide Emission:‘Equivalent Carbon Dioxide’ refers to an amount of emissions describing, for agiven mixture, an equivalent amount of CO2 that would have the same globalwarning potential measured over a timescale generally of 100 years [13].
4 Inventory Assessment of Flow-Materialin the Concentration Phase of PGM Recovery
The concentration phase of PGM recovery accounts for significant solid and liquidemissions ending at tailings dams dug in the surroundings. Because of the of soilpermeability, liquid residues end up expanding to neighboring environment. Acidmine drainage is one of the residues that affects and contaminates the groundwatersources and identified as one of the most important issues with the concentratesphase of platinum recovery process.
The Inventory Flow-Chart: 400 g of PGM per tonne of Concentrates (Fig. 4).Concentration phase uses large quantities of water; and this calls for on-site
recycling wastewater, which in turn causes direct and indirect emissions due to theuse of a certain amount of energy from emitting resources in CO2 and the use ofchemicals. It is to be noted that South Africa is 88 % based coal burning plantpower generation.
Product Material
Inputs (including
reuse & recycle from
the working single
stage)
Single Stage or
Unit Operation
Process Materials, Reagents,
Solvents and Catalysts (including reuse & recycle from another)
Fugitive &
Untreated
WasteReuse/Recycle
Reuse/Recycle
Primary Product
Useful Co -product
Waste
Energy
Fig. 3 Input/output of single stage or unit operation or unit process in a flow chart. Source [10]
Ore Processing by PGM Concentration Process … 279
5 Individuals and Overall Equivalent Carbon Dioxide(CO2-eq) Emissions
The following Table 3 shows a total amount of carbon equivalent of 1574.96 kgCO2-eq to process one metric ton of ore by concentration. The masses displayed inthe column “product” together with the designated constituents, are apparentweights which are in relation to the molecular masses of these constituents.
They are the total masses of the constituents in the entire life cycle analysis(mining-off-gas. The column “share”, however depicts, by a length, the amount ofCO2-eq emissions emitted by each constituent in the phase.
Fig. 4 Flow-material in the concentration phase of PGM recovery process [8]
280 J. Mabiza-ma-Mabiza and C. Mbohwa
6 Results
The most significant CO2-eq emissions in the concentration process of PGMrecovery, as referred in Table 3, are, in the order of magnitude, attributed towastewater treatment (454.65 kg CO2-eq), crushed rocks (454.65 kg CO2-eq),Sulphur (344.82 kg CO2-eq), blown air (121.88 kg CO2-eq) and the sand(121.88 kg CO2-eq). Blown air represents indirect CO2-eq due to the energy used topump slurry from milling to comminution. Comminution consists of grinding theslurry ore to powder (Fig. 3). It is also important to observe that wastewatertreatment can likely transfer reagents (PGM collectors) to the tailings dam, with theunfortunate occurrence acid mine drainage.
7 Conclusion
South African PGM producers have set up appropriate management systems tai-lored to ISO 14001 standards. These also track legal compliance and preventpollution [9]. Nevertheless real damage to environment are very much involved inthe production of the platinum precious metals with tangible adverse emissions tothe surroundings of processing plants which respond to disturbances namely, airpollution with volatile organic compounds and dust emission, noise pollution, acidmine drainage containing chemicals interacting with local populations, affectinghuman health, underground water, livestock, fauna, flora and forcing countrysideexodus.
Table 3 Equivalent carbon dioxide emissions in the concentration phase [8]
Ore Processing by PGM Concentration Process … 281
Tab
le4
Recapitu
latio
nof
CO2-eq
emission
sin
processing
ametrictonof
orefrom
miningto
off-gashand
lingph
ase[8]
Prod
uct
Relativemass
(kg)
CO2-eq
(kg)
Mining
Ore
concentration
Smeltin
gCon
verting
Off-gas
hand
ling
Total
Blownair
40.00
42.65
121.88
115.49
34.38
1.43
E−15
314.40
Chrom
ium
oxide.
Flakes
144.32
3.52
10.05
121.41
75.33
−5.16
E−15
210.31
Cob
alt
2.36
0.25
0.72
8.70
90.60
6.33
E−16
100.27
Cop
per
49.11
1.48
4.23
51.07
314.37
1.74
E−14
371.15
Crushed
rocks
779.79
138.29
454.65
592.94
Dust
0.20
1.26
1.26
Fayalite
178.01
12.87
36.79
467.46
355.30
−1.02
E−13
872.42
Gas
flow/particles
2339
.22
8.34
23.84
287.95
94.38
401.01
815.52
Iron
oxide
119.70
4.78
13.65
164.89
118.18
6.43
E−14
301.50
Lim
estone
177.36
177.36
Magnesium
oxide.
Flakes
7.62
0.48
1.37
16.50
44.59
−4.36
E−15
62.94
Nickel
52.67
4.22
12.06
145.65
355.22
3.58
E−14
517.15
PGM
1.12
0.07
0.21
2.57
83.34
1.90
E−16
86.19
Polysulphide.Sealingcompo
und
60.33
3.53
10.09
144.94
60.81
219.37
Sand
2.00
17.43
79.99
4.39
101.81
Second
arysulphu
r65
0.00
102.35
344.82
126.96
574.13
Sulphu
ricacid
249.86
2.03
5.80
70.09
23.03
107.80
208.75
Sulphu
rdiox
ide
0.14
0.06
0.16
1.92
0.63
2.71
5.48
Wastewater
treatm
ent.Particle
boardprod
uctio
nefflu
ent
103.89
138.29
454.65
177.36
770.30
Total
equivalent
carbon
diox
ide(kgCO2-eq)
481.90
1574
.96
2084
.71
1650
.16
511.52
6303
.25
282 J. Mabiza-ma-Mabiza and C. Mbohwa
8 Recapitulation of CO2-eq Emissions in Processing OneMetric Ton of Ore for the Recovery of PGM
See Table 4.
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Ore Processing by PGM Concentration Process … 283
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