voller 117 Comminution Linking the blast furnace to

voller 1/17 Comminution: Linking the blast furnace to the production of loess. Vaughan R. Voller From Kelly and Spottiswood Intro Min Proc, Wiley, 1982 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

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

Why is important to Minnesota voller 3/17 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

voller 4/17 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 Crushing http: //www. aggdesigns. com/ Cone-Crusher-info. htm#section 1 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

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

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

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

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

Think of grinding operation where a feed is put into a batch ball mill voller 9/17 and worked on for a given length of time Assume that Size distribution after A give time is characterized by Wj(t) (j =1, --n) number if size intervals Wj(t) weight fraction in interval j From Kelly and Spottiswood Intro Min Proc, Wiley, 1982 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

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

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

voller 12/17 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 imapct No abrasion No saltation Can We modify to account for abrasion-saltation ?

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

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

voller 15/17 A size sorting Long-Profile population balance model Breakage: Particles beak by impacts and abrasion—selection a function of Slope S x 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) Equilibrium: Transport process are sufficient to maintain location of a given size interval between breaking events 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

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

Comminution: Linking the blast furnace to the production of loess. Vaughan R. Voller The breaking of particles is an important component the dynamics of the Earth’s surface. 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 the work in mineral engineering could be applied in understanding earth surface processes voller 17/17