Milling facilityType of grinding millAdvantagesDisadvantagesJustification

Ball Mill Used in secondary closed circuit Robust and simple Small size Low energy consumption High risk of over grinding primary feed grinding size up to 15mm High order of crushers needed

SAG mill is chosen as the primary mill over the other tumbling equipments due to its features of large capacity ores handling, fulfill the criteria of processing coarse ore size of 20000 m and equipped with grinding media to achieve a consistence and finer ores. Over- grinding is prevented due to its capability to process ores at short retention time.

Rod Mill Coarse grinding with top size control without classification Small size Low energy consumption Narrow particle size distribution Low plant capacity with < 200t/h Primary feed grinding size up to 50mm High order of crushers needed

Autogeneous Mill Coarse grinding up to 400mm feed size High capacity (short retention time) Low order of crushers needed Sensitive to feed composition Inconsistence grinding behavior Limited to certain ores with specific harness and abrasiveness Large size High energy consumption

Semi-Autogeneous Mill Coarse grinding up to 400mm feed size Higher capacity than autogeneous mill (short retention time) Less sensitive to feed composition Consists of grinding media (steel grinding ball) Low order of crushers needed

Large size High capital cost Relatively high energy consumption

AssumptionsClosed circuit design with wet grinding is employed in the process to handle high load capacity of ores. It is expected to achieve low power consumption per ton of product, ensures product size required fulfilled and eliminate the possibility of over-grinding of ores with the use of classifier like hydrocyclones. Combination of SAG mill and ball mill are chosen as the design circuit in the aim to achieve low operating cost and maximize the performance.

Preliminary sizing for ball mill and sag mill procedureNotation

Step 1: E= 10 x Wi Step 2: Determination of Wic, WiBM, WiRM with given size range from online resourcesStep 3: Ebm = 10 x Wic + [10 x WiRM + 10 x WiBM x EF5BM ] x EF4BMEF4BM = Step 4: Etotal = 1.15 x EStep 5: ESAG = [ 10 x Wic + 10 x Wic x EF4RM + 10 x Wic x EF4BM x EF5 ] x 1.25 - 10 x Wic x EF4BM x EF5EF4RM = Step 6: Ebm = Etotal - ESAGStep 7: Total SAG Motor Power= (ESAG x tonnes/hour)/0.985/0.90Step 8: Total Ball Mill Motor Power = (EBM x tonnes/hour)/0.985/0.94Step 9: Determination of effective grinding length, EGL Step 10: Estimation of dimension from vendor catalogueE = Specific energy consumption, kWh/tonnesWi = work index of bauxite oreP80= 80% passing size of the feed, F80= 80% passing size of the product, Wic = Crushing work indexWiBM = Ball mill work indexWiRM = Rod mill work indexEF5BM = Factor for ball milling (only applicable for P80 < 75) EF4BM = Factor for ball milling Etotal= Total energy consumption of SAG and ball mill circuitPc= primary crusher product size PR= rod mill product size T80= Synthetic transfer size between the SAG mill and ball mill

Information given and calculated valueResult from vendor catalogue

Data given and additional infoBauxite bond index, Wi = 14Bauxite F80 = 20000 m; P80 = 300 mTypical size ranges for bond work index testsWic: 100000 10000 m (F80-P80)WiRM: 10000 2100 m (F80-P80)WiBM: 2100 -100 m (F80-P80)Calculated valueE = 7.09 kWh/tWic = 103.733 WiRM = 59.999WiBM = 9.073EF4BM = 1.13EF4RM = 1.05Etotal = 38.74 kWh/tESAG= 33.78 kWh/tEbm = 4.96 kWh/tTotal SAG mill motor mill = 22MWTotal Ball mill motor power = 3MWEGL = 22.24ft

SAG mill: 23MW motor output power (ring motor drive) , 42ft x 24ft (D x L) Ball mill: 3.356 MW motor output power, 16.5ft x 27ft (D x L)

Hydrocyclone

Purposes and justifications

Sizing AssumptionsThe overflow of particles are assumed to be 80% passing

Type of grinding millAdvantagesDisadvantagesJustificationPreliminary Sizing Result

Ball Mill Used in secondary closed circuit Robust and simple

High risk of over grinding primary feed grinding size up to 15mm

Rod Mill Coarse grinding with top size control without classification

Low plant capacity with < 200t/h Primary feed grinding size up to 50mm

Autogeneous Mill Coarse grinding up to 400mm feed size High capacity Sensitive to feed composition

Semi-Autogeneous Mill Coarse grinding up to 400mm feed size Higher capacity than autogeneous mill Less sensitive to feed composition (czm)

Justification