1. voller Comminution: Linking the blast furnace to the production of loess. Vaughan R. Voller What is Comminution From Wikipedia: Comminution is one of the four main groups of mechanical processing and describes the movement of the particle size distribution (grains, drops, bubbles) into a range of finer particle sizes (The other groups are agglomeration, separation and mixing). Explain Some Basic Comminution Processes and provide landscape examples Show why it is important to the health and wealth of Minnesota Develop some basic comminution laws Describe the so called “population balance” model Demonstrate two “toy” landscape models based on population balance concept From Kelly and Spottiswood Intro Min Proc, Wiley, 1982 1/17

2. voller Modes of Comminution Particle size From Kelly and Spottiswood Intro Min Proc, Wiley, 1982 Glacial abrasion Debris Flow Saltation Sklar and Dietrich weathering Comminution in Landscape Dynamics x Size Sorting 2/17

3. voller Why is important to Minnesota The US Steel Industry produces about 1/8 th of World’s Steel The Columbia Encyclopedia, Sixth Edition. Copyright © 2001-05 Columbia University Press. On the order of ½ of the iron ore comes from Minnesota’s Iron Range Ore has been shipped from Minnesota since the late 1890’s Up until the 40’s this was high grade Hematite Ore Fe 2 O 3 When supplies became exhausted switched to Taconite --LOW grade mixture of Silica and Magnetite Fe 2 O 4 This required processing the ore to create suitable feed for The blast furnace 3/17

4. voller The Taconite Process: Developed by E.W. Davis at the University of Minnesota Run of mine ~25 % Fe-need to reduce to grain size of magnetite http://www.aggdesigns.com/ Cone-Crusher-info.htm#section1 Crushing grinding At grain size Magnetite can Be seperated Product too small and wrong chemical composition so agglomerated and indurated Fe 2 O 4  Fe 2 O 3 Product can be shipped and used Directly in BF 4/17

5. voller Particle size Two Things we would Like to Know For a Given Energy What is the Reduction in Particle Size— The Comminution Laws For a Given “Communition Event” How does size distribution change From Kelly and Spottiswood Intro Min Proc, Wiley, 1982 5/17

6. voller From Kelly and Spottiswood Intro Min Proc, Wiley, 1982 The Comminution Laws Consider a simplistic communtion operation that for each event reduces the particle size by a factor of 1/2 Rittenger (1867): xFxF After q events Kick (1885): Energy for each event  E=Constant After q events E = q  E 6/17

7. voller Rittenger (1867): Kick (1885): Energy for each event  E=Constant A general Law For general case x—an average part. size Log Particle Size Log Energy Input Grind Limit Kick Rittenger Crushing Abrasion After Hukki Instructive to look at energy as A function of size reduction for quartz Rittenger works best at describing Abrasion- Kick at describing crushing Hukki suggested combined law Voller shows if Linear combo of Kick and Rittenger 7/17

8. voller Particle size The comminution laws Say how the “average” Particle sizes changes for a given Energy input But how does the Particle size distribution change For this we use A Population Balance Model From Kelly and Spottiswood Intro Min Proc, Wiley, 1982 8/17

9. voller From Kelly and Spottiswood Intro Min Proc, Wiley, 1982 Assume that Size distribution after A give time is characterized by W j (t) (j =1, --n) number if size intervals W j (t) weight fraction in interval j For a given grinding “event” We define a A Selection Function k(j) ----fraction of particles broken out of interval j A Breakage Function b(j,i) ---fraction of particles broken from interval i (<j) that end up in j Think of grinding operation where a feed is put into a batch ball mill and worked on for a given length of time 9/17

10. voller From Kelly and Spottiswood Intro Min Proc, Wiley, 1982 Between two consecutive “events” we can construct a population balance Amount remaining in j Amount entering j 10/17

11. voller Pop Bal Model Possible forms for Breakage and Selection functions Derive form Comminution Laws 11/17

12. voller Current version of the model is a BATCH model In land scale dynamics-could relate ???? to “Cohort” Debris flow with NO breakage or erosion (saltation) due to contacts with basement saltation abrasion imapct No Can We modify to account for abrasion-saltation ? 12/17

13. voller Base Rock Model Parameters for Debris Flow Mass Balance  = K= selection Fraction of selected particles that break by impact with basement Assumption: Breakage products the same for particle-particle impacts and particle-basement impacts  = Volume of liberated from Base = Volume Impacting Base Related to Bitter erosion Law ??? 13/17

14. voller A proposed The Debris Flow Mass Balance saltation abrasion imapct Amount remaining in j amount entering j via particle-particle impacts amount entering j via particle-bed impactsamount entering j liberated from bed As written  and  are constant but could be functions of slope and particle size 14/17

15. voller A size sorting Long-Profile population balance model x Breakage: Particles beak by impacts and abrasion—selection a function of Slope S Equilibrium: Transport process are sufficient to maintain location of a given size interval between breaking events Location: in size distribution an given size interval is associated With a location in the landscape Fines: the smallest size interval exits system (sub-marine deposit) Uplift: Mass is maintained in system by adding fine mass created in an event to mass of largest particel size interval before next event Profile: Depth of profile is proportional to weight fraction of size interval 15/17

16. voller x A size sorting Long-Profile population balance model After repeated “events” an initial flat straight profile approaches A steady sate profile with an identified erosional and depositional component 16/17

17. voller The breaking of particles is an important component the dynamics of the Earth’s surface. Comminution: Linking the blast furnace to the production of loess. Vaughan R. Voller The breaking of ores is a critical process in mineral processing--- The economic importance of this industry has led to extensive study of how rocks break (comminution) The aim of this seminar has been to show how the work in mineral engineering could be applied in understanding earth surface processes 17/17