Developments in Solid-state Physics and Chemistry
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Environmentally Safe Gold Extraction James D. Mavis, Jr. CH2M HILL A block flow diagram of Homestake's McLaughlin project gold recovery process. Homestake Mining Company's ef- forts to process refractory gold ore from the McLaughlin Mine led to an uncon- ventional treatment train to improve gold recovery. The gold at the McLaughlin Mine is highly disseminated throughout the sulfide phase, which made it nec- essary to improve gold leaching char- acteristics by oxidizing the sulfide. Environmental and economic consid- erations led Homestake to install a pressure slurry oxidation (autoclaving) step between the milling and carbon-in- pulp extraction circuits to free to gold. Figure 1 is a block flow diagram of the gold recovery process. CH2M HILL worked closely with Homestake's engineering and environ- ment groups to assess how various process alternatives would affect emis- sions to the atmosphere and the prop- erties of tailings. Preliminary estimates of atmospheric release rates and tail- MINE .. ings composition were prepared from early flowsheets for disclosure in the environmental impact report. This infor- mation helped Homestake to select au- toclaving as the process that would achieve the results required in the most economical and environmentally sound way. The absence of significant releases to the atmosphere was due primarily to the use of autoclaving instead of roast- ing. Roasting was dropped from con- siderationbecause the process required installation of expensive emission con- trol equipment, and because autoclav- ing the ore slurry at 320°F avoided the release of sulfur oxides and volatile metals that are normally associated with Developments in Solid-state Physics and Chemistry Vyacheslav Yelyutin, Anatoli Manukhin and Yuri Pavlov V.S.S.A. Academy of Sciences _ Editor's Note: This story was submitted to the Journal of Metals by the Novosti Press Agency in Moscow. The Moscow Steel and Alloys Insti- tute has recently made a discovery re- lated to the fields of solid-state physics and chemistry, which is being applied in ferrous and nonferrous metallurgy. Experiments have indicated the exis- tence a hitherto unknown regularity in the pyrometallurgic reduction of ele- ments out of oxides which leads simul- taneously to a change in the conduction properties of oxides (from extrinsic to intrinsic)and their reactivity. The change in a conduction type is preconditioned by a higher concentration of free elec- trons in the crystalline lattice of semi- conductor oxides. By investigating the interaction be- tween metallic oxides and carbon and hydrogen (basic reducing agents in fer- rous and nonferrous metallurgy), re- searchers are attempting to identify the electronic state solid crystalline oxides and manifest their reactivity with re- spect to carbon and hydrogen, the other reducing agents. The temperature trig- gering off a noticeable interaction be- tween an oxide and carbon was taken 48 as the main criterion in experiments. Unique methods of using tracer atoms (radiocarbon C14, oxygen stable iso- tope 018), a structurally sensitivemethod of measuringelectric resistance and gas chromotography were developed to conduct experiments in a broad range of temperatures. It was established that the start of interaction in the oxide-car- bon system is primarily determined by the physical properties of a metallic ox- ide. Taking into account the semiconduc- tor nature of metallic oxides, further ex- periments were directed at studying the temperature dependence of the electric resistance of various oxide samples and the comparison of their semiconductor properties with their reactivity assessed by values of temperature triggering in- teraction between an oxide and carbon. These investigations discovered im- portant regularities establishing a link between physical (semiconductor) and chemical properties of metallic oxides, making it possible to examine the elec- tronic mechanismof their interaction with a reducing agent. It was established that the temperature starting interaction practically coincides with a radical change in the electronic state of ox- ides-their transition into a state of in- trinsicconduction. In other words,carbon starts reducing a metallic oxide when the concentration of free electrons in its crystalline lattice is highest. A close link was also detected be- tween the reactivity of metallic oxides and their fundamental semiconductor property-a breadth of the forbidden zone. The greater its value, the higher is the temperature triggering interaction between an oxide and a reducer. Influence of various admixtures (ad- ditives) on physical (semiconductor) and chemical (reactivity) properties of me- tallic oxides is very important. Investi- gations have shown that oxide additive agents to the main oxide simulta- neously influence both electrophysical properties and its reactivity. The influ- ence of admixtures depends not only on their concentration but also on their nature. If the thermodynamic strength of the added admixture is higher (a hard- to-reduce oxide) than the main oxide, the temperature of its transition into a state of intrinsic conduction rises, the breadth of the forbidden zone grows and reactivity lessens. On the other hand, oxide additive agents having a lesser thermodynamic resistance to oxidation JOURNAL OF METALS. January 1987
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Transcript of Developments in Solid-state Physics and Chemistry
~Features
Environmentally Safe Gold ExtractionJames D. Mavis, Jr.CH2M HILL
A block flow diagram of Homestake's McLaughlin project gold recovery process.
Homestake Mining Company's efforts to process refractory gold ore fromthe McLaughlin Mine led to an unconventional treatment train to improve goldrecovery. The gold at the McLaughlinMine is highly disseminated throughoutthe sulfide phase, which made it necessary to improve gold leaching characteristics by oxidizing the sulfide.Environmental and economic considerations led Homestake to install apressure slurry oxidation (autoclaving)step between the milling and carbon-inpulp extraction circuits to free to gold.Figure 1 is a block flow diagram of thegold recovery process.
CH2M HILL worked closely withHomestake's engineering and environment groups to assess how variousprocess alternatives would affect emissions to the atmosphere and the properties of tailings. Preliminary estimatesof atmospheric release rates and tail-
MINE
-1'~ PIT ~_",.~ .. ",~
ings composition were prepared fromearly flowsheets for disclosure in theenvironmental impact report. This information helped Homestake to select autoclaving as the process that wouldachieve the results required in the mosteconomical and environmentally soundway.
The absence of significant releases
to the atmosphere was due primarily tothe use of autoclaving instead of roasting. Roasting was dropped from consideration because the process requiredinstallation of expensive emission control equipment, and because autoclaving the ore slurry at 320°F avoided therelease of sulfur oxides and volatilemetals that are normally associatedwith
Developments in Solid-state Physics and ChemistryVyacheslav Yelyutin, Anatoli Manukhin and Yuri PavlovV.S.S.A. Academy of Sciences _
Editor's Note: This story was submitted tothe Journal of Metals by the Novosti PressAgency in Moscow.
The Moscow Steel and Alloys Institute has recently made a discovery related to the fields of solid-state physicsand chemistry, which is being appliedin ferrous and nonferrous metallurgy.Experiments have indicated the existence a hitherto unknown regularity inthe pyrometallurgic reduction of elements out of oxides which leads simultaneously to a change in the conductionproperties of oxides (from extrinsic tointrinsic)and their reactivity. The changein a conduction type is preconditionedby a higher concentration of free electrons in the crystalline lattice of semiconductor oxides.
By investigating the interaction between metallic oxides and carbon andhydrogen (basic reducing agents in ferrous and nonferrous metallurgy), researchers are attempting to identify theelectronic state solid crystalline oxidesand manifest their reactivity with respect to carbon and hydrogen, the otherreducing agents. The temperature triggering off a noticeable interaction between an oxide and carbon was taken
48
as the main criterion in experiments.Unique methods of using tracer atoms(radiocarbon C14, oxygen stable isotope 018), a structurally sensitivemethodof measuringelectric resistance and gaschromotography were developed toconduct experiments in a broad rangeof temperatures. It was established thatthe start of interaction in the oxide-carbon system is primarily determined bythe physical properties of a metallic oxide.
Taking into account the semiconductor nature of metallic oxides, further experiments were directed at studying thetemperature dependence of the electricresistanceof various oxide samples andthe comparison of their semiconductorproperties with their reactivity assessedby values of temperature triggering interaction between an oxide and carbon.
These investigations discovered important regularities establishing a linkbetween physical (semiconductor) andchemical properties of metallic oxides,making it possible to examine the electronic mechanismof their interaction witha reducing agent. It was established thatthe temperature starting interactionpractically coincides with a radicalchange in the electronic state of ox-
ides-their transition into a state of intrinsicconduction. In other words,carbonstarts reducing a metallic oxide whenthe concentration of free electrons in itscrystalline lattice is highest.
A close link was also detected between the reactivity of metallic oxidesand their fundamental semiconductorproperty-a breadth of the forbiddenzone. The greater its value, the higheris the temperature triggering interactionbetween an oxide and a reducer.
Influence of various admixtures (additives) on physical (semiconductor) andchemical (reactivity) properties of metallic oxides is very important. Investigations have shown that oxide additiveagents to the main oxide simultaneously influence both electrophysicalproperties and its reactivity. The influence of admixtures depends not onlyon their concentration but also on theirnature. If the thermodynamic strengthof the added admixture is higher (a hardto-reduce oxide) than the main oxide,the temperature of its transition into astate of intrinsic conduction rises, thebreadthof the forbidden zone grows andreactivity lessens. On the other hand,oxide additive agents having a lesserthermodynamic resistance to oxidation
JOURNAL OF METALS. January 1987
roasting operations. Sulfur oxide releases from the autoclave vents are notsignificant because iron dissolved in theacidic autoclave slurry catalyzes thecomplete-oxidation of sulfide to sulfateinstead of more volatile sulfur dioxide.
In other parts of the process atMcLaughlin, atmospheric emissions arevery similar to more conventional goldrecovery operations. However, the regulatory climate in the environmentallysensitive area of California surroundingthe mine made it necessary to forecasttypes and quantities of substances thatwould be released from all anticipatedair emission sources, and to verify thoseforecasts by performing source tests onthe commercial operating facility. CH2MHILL successfully completed the sourcetesting program following plant startupand stabilization in 1985. This is believed to be the first time a commercial
gold recovery facility has been so exthe atmosphere.
The McLaughlin Mine gold recoveryprocess also has several other favorable attributes, contributed in part by autoclaving. One important feature is thatby oxidizing the sulfide fraction of theore, the potential for acid formation inthe tailings is removed. This eliminatesthe need for extraneous measures forcontrol such as enhanced containmentstructures.
Another benefit provided by autoclaving is a reduction in reagent consumption in the carbon-in-pulp (CIP)circuit. This is achieved by bypassingreagent-consuming constituents that aredissolved during autoclaving around theCIP circuit (via the decant neutralization/precipitation circuit in Figure 1). Anadditional benefit is that, because reagent consumption is reduced, process
tailings contain lower concentrations ofresidual reagents. These levels are fursuming components are recombinedwith CIP tailings for placement in thetailings impoundment.
The process at the McLaughlin Minehas earned acceptance for preservingenvironmental quality in an environmentally sensitive region of Californiawhile proving to be efficient and economic as well.
If you want more information on this subject,please circle reader service card number 77.
UMC Book Review Program
Metallurgical Calculations - Part IVA.E. Morris, James StephensonUniversity of Missouri-Rolla Rolla Research Center, U.S. Bureau of Mines
The exclusive book reviews appearing in Journal of Metals each month are anexceptional member service. A cooperative effort with the University Materials Council (UMC) enables the Journal to maintain the most comprehensive review programanywhere in the field of materials engineering. The UMC represents the departmentheads of the metallurgy and materials science schools in the United States.
The UMC book review program operates through designated contact persons atparticipating universities, who disseminate review books acquired by the Journal. Ifyou are interested in being part of our mailing list, please contact Shirley Miller at(412) 776-9070.
than the main oxide lower the temperature of its transition to intrinsic conduction, reduce the breadth of theforbidden zone and raise the reactivityof oxides. The study of the admixtureinfluence on properties of metallic oxides has clearly revealed a link betweenelectrophysical properties and reactivity. The established regularity of admixture influence on electrophysicalproperties and the reactivity of metallicoxides makes it possible, in principle,to control the process of interaction between metallic oxides and other agents.
Researchers have revealed the common electronic nature of the conductivity of metallic oxides and their reactivity.Their work indicates that a rise in theconcentration of free electrons in thesystem, necessary to intensify physicaland chemical processes, can beachieved by introducing donor additivesand other physical methods of influencebesides traditional heating. This discovery can be applied to intensify physicaland chemical processes in metallurgy,chemical technology, the production ofcomposites, semiconductor materialsand other economic sectors.
If you want more information on this subject,please circle reader service card number 78.
JOURNAL OF METALS. January 1987
MAINFRAME SYSTEM:SHIMPO·GOTO
SHIMPO-GOTO Version III is writtenin FORTRAN 77 and is used for calculating molar amounts of variousphases at equilibrium in large chemicalsystems at a given temperature andpressure. The package allows a moreflexible input than Versions I or II. Inaddition, heat balance calculations maybe done by providing input of molal heatcontents, temperatures of transformation for components below their reaction temperature, and heat contents ofcharge components. All data must becarefully prepared before execution, andthere is no way to change data after
entry because of batch processing. Mostconference attendees found the program to be the most difficult to evaluate,even with the assistance of workshoppersonnel. Once correct input of datawas achieved, the results were quicklyand accurately attained.
The has been the fourth installment ofan eight-part series which is examiningsome of the programs featured at theComputer Software for MetallurgicalCalculations Conference, which tookplace late in 1985 at the University ofMissouri-Rolla.
If you want more information on this subject,please circle reader service card number 76.
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