WO 00/12996 PCT/AU99/00703 APPARATUS FOR CALCULATING DENSITY/SPECIFIC GRAVITY OF SLURRY 5 The present invention relates to an apparatus and a method for use by mineral plant operators to determine a range of properties of mineral solids and slurries. 10 Most mineral processing plants include mineral processing operations on slurry streams of water and solids transported through circuits via pumps and pipelines. It is important for plant operators to measure the properties 15 of slurries at different stages of a plant operation in order to monitor the performance of the circuits in the plant. It is known to monitor the performance of a plant 20 by calculating: (i) slurry density, ie the weight of the slurry per unit volume; 25 (ii) specific gravity of a slurry, ie the ratio of the density of the slurry and the density of water; (iii) slurry percent solids, ie weight of solids 30 in a slurry per unit weight of slurry or per unit volume of slurry; and (iv) grams solid per litre of slurry sample. 35 A widely used option for calculating these properties is a spring balance which includes a central spring, a measuring bucket that can be suspended from the WO00/12996 PCT/AU99/00703 - 2 spring, a pointer that is deflected proportionally to-the weight of a sample in the bucket, and a display mechanism for providing a reading of the specific gravity or other properties of the sample based on the position of the 5 pointer in relation to the display mechanism. One limitation of spring balances with slurries is that the operation of the balances is based on the assumption that the specific gravity of the process 10 solution is always 1.0. This characteristic limits the use of spring balances to simple water-solids systems. A further limitation is that spring balances are mechanical devices containing a number of unprotected 15 moving parts and are susceptible to corrosion by and clogging with process materials with consequent loss of accuracy and functionality. The operation of spring balances relies on the sustained performance of the spring and a drive gear for the pointer. Distortion of the spring 20 can be corrected by a coarse adjusting screw, but again the serviceability of this simple calibration device is susceptible to the harsh operating conditions that are typically found in the mineral processing environment. Spring balances are often ultimately discarded as service 25 and repair is difficult. A further limitation is that spring balances are bulky in that a machine of a useful size is both heavy and awkward to carry and position for satisfactory use. 30 A further limitation is that spring balances are prone to structural vibration which makes interpretation of the displayed results difficult. This is a particularly significant operational limitation because the most common 35 points of use in a mineral processing circuit are adjacent to mills, pumps and screens where structural vibration is commonplace.

WO00/12996 PCT/AU99/00703 - 3 A further limitation is that the display mechanism of spring balances consists of interchangeable paper face sheets which allow operators to determine the 5 solids concentration of a sample over a range of selected particle densities and a number of different face sheets are required to span the range of typical mineral densities. Changing the range of the readout is accomplished by changing the paper dial on balances. This 10 operation exposes the pointer to damage, thus compromising the accuracy of the balances. A further limitation is that accuracy of spring balances is low. The balances are an analogue device which 15 is characterised by the following requirements for ideal operation: (i) clean conditions; 20 (ii) absence of external vibration; (iii) invariant solution density of 1.0; and (iv) good lighting. 25 In addition, the quality of the output of spring balances is compromised by the following: (i) coarse calibration function; 30 (ii) non-continuous solids specific gravity scales; and (iii) non-linear output scales which are 35 partially obscured by the width of the pointer.

WO00/12996 PCT/AU99/00703 - 4 An object of the present invention is to provide an apparatus for calculating one or more of density, specific gravity, grams solid per litre of slurry, and slurry percent solids of a slurry which is not subject to 5 the limitations of spring balances described above. According to the present invention there is provided an apparatus for calculating the density and/or the specific gravity of a sample of a slurry which includes 10 solids in a liquid, which apparatus includes: (i) an electric means for measuring the weight of a known volume of the slurry; and 15 (ii) an electronic computing means for calculating the slurry density and/or the specific gravity of the slurry from the measured weight of the slurry and the known volume of the slurry sample. 20 It is preferred that the electric measuring means be a load cell or a strain gauge. It is preferred that the electronic computing 25 means includes a means for confirming a stored value of the known volume of the slurry or for inputting another value of the volume. It is preferred that the apparatus also be 30 capable of calculating the percent solids of the slurry and/or the grams solid per litre of the slurry. It is preferred particularly that the electronic computing means includes a means for confirming a stored 35 value of the density of the liquid component of the slurry or for inputting another value of the liquid density for use in calculating the percent solids of the slurry and/or WO00/12996 PCT/AU99/00703 -5 the grams solid per litre of the slurry. It is preferred more particularly that the value of the liquid density be calculated from the weight of a 5 known volume of the liquid measured by the electric measuring means. It is preferred that the electronic computing means includes a means for confirming a stored value of the 10 specific gravity or the density of the solids component of the slurry or for inputting another value of the solids density for use in calculating the percent solids of the slurry and/or the grams solid per litre of the slurry. 15 It is preferred that the electronic computing means includes a means for confirming a stored value of the weight of a container for holding the slurry to be tested or for inputting another value of the container weight so that the value of the container weight can be taken into 20 account in calculations of the slurry density and other parameters by the electronic computer means. It is preferred particularly that the value of the container weight be a value measured by the electric 25 measuring means. According to the present invention there is provided an apparatus for calculating any one or more of the parameters of the density of a slurry, the specific 30 gravity of the slurry, the percent solids of the slurry, and the gram solid per litre of the slurry, which slurry includes solids in a liquid, which apparatus includes: (i) an electric means for measuring the weight 35 of a volume of the slurry; and (ii) an electronic computing means for WO 00/12996 PCT/AU99/00703 - 6 calculating one or more of the parameters from the measured weight and data on the properties of the slurry, the solids, and the liquid required for the calculation 5 that has already been inputted into and stored in the electronic computer means. The inputted and stored data includes the volume of the slurry, the density of the solids, and the density 10 of the liquid. According to the present invention there is also provided a method of calculating the density and/or the specific gravity of a slurry which includes solids in a 15 liquid, which method includes the steps of: (i) confirming a value of a volume of a slurry sample to be tested, which value is stored in an electronic computing means, or 20 inputting another value of the slurry volume into the electronic computing means; (ii) measuring the weight of the slurry sample using an electric measuring means; and 25 (iii) calculating the slurry density and/or the specific gravity of the slurry using the electronic computing means and the confirmed or inputted value of the slurry 30 volume and the measured value of the weight of the slurry sample. It is preferred that the method also includes the option of calculating the percent solids of the slurry 35 and/or the grams solid per litre of the slurry. In order to make calculations of the slurry WO00/12996 PCT/AU99/00703 - 7 percent solids and/or grams solid per litre of the slurry it is preferred that the method includes: (i) confirming a value of the density of the 5 liquid component of the slurry, which value is stored in the electronic computing means, or inputting another value of the liquid density into the electronic computing means; and 10 (ii) confirming a value of the density of the solids component of the slurry, which value is stored in the electronic computing means, or inputting another value of the 15 solids density into the electronic computing means. The present invention is described further by way of example with reference to the accompanying drawing which 20 is a flow chart illustrating the basic unit operation of a preferred embodiment of a balance in accordance with the present invention. The preferred embodiment of the balance of the 25 present invention includes a load cell/strain gauge, a programmed microchip that can perform a series of calculations on data generated by the load cell/strain gauge and on data inputted by an operator, a keypad for inputting data and initiating functions, and a display. 30 The keypad includes keys numbered 0-9 for data entry and the following marked keys. ZERO 35 Initiates the Zero function. This function zeros the load cell output for the container that holds a sample WO00/12996 PCT/AU99/00703 - 8 of slurry to be tested. When selected, the current Zero value is displayed and the operator may choose to accept the current value by selecting the ENTER key or to perform the Zero Set function by selecting the ZERO 5 key. The Zero Set parameter is retained in non-volatile memory and may be modified by selecting the ZERO key. 10 CAL Initiates the Calibrate function. This function allows the entry or calculation of the density of the liquid component of the slurry samples to be tested in 15 subsequent operations. The Calibrate (Liquid Density) parameter is retained in non-volatile memory and may be modified by selecting the CAL key. 20 When selected, the calibrate screen displays the current setting, the operator may choose to accept the current value by selecting the ENTER key or enter a new value by keying in the new value on the numerical 25 keypad, followed by selecting the ENTER key. If the liquid density is unknown, the liquid density can be calculated by selecting the CAL key. The new calibrate value is displayed and accepted by selecting the ENTER key. 30 CALC When selected, this key calculates the following properties of the slurry being tested and displays the 35 results of the calculations: - Slurry Density in grams per litre (gpl) WO00/12996 PCT/AU99/00703 - 9 - Slurry percent solids (by weight) - Slurry percent solids (by volume) - Grams solid per litre of slurry(gpl) 5 SUB Provides access to the Sub-Routine menu. The Sub Routine menu enables the operator to select and execute one of the following sub-routines: 10 (1) % Passing Screen Size (2) Solid Specific Gravity (SG) (3) Variable Volume Mode 15 Sub-Routine 1 The % passing Screen Size sub-routine calculates the Mass % passing a particular screen size, based on three weighed samples ( plus the Zero step). The sequence of 20 events for the subroutine is as follows: (1) Zero Step (Zero load-cell) (2) Calibrate (Liquor Density) (3) Sample 1 (Initial Slurry Density) 25 (4) Sample_2 (Screened Slurry Density) Both events 1 & 2 use the standard ZERO and CALIBRATE function screens. The current values stored in non volatile memory can be used or the operator can re 30 calculate both values. The operator is prompted for Sample_1 and Sample_2. Pressing the ENTER key after the sample_ 1 has been 35 placed on the load-cell will initiate the entry of sample_l, followed by a prompt for Sample_2.

WO00/12996 PCT/AU99/00703 - 10 Pressing the ENTER key after sample_2 has been pl-aced on the load-cell will initiate the entry of sample_2. After the entry of sample_2, the sub-routine result 5 will be calculate and displayed as: SUB-ROUTINE : 1 SLRY 1 DENSITY : xxx SLRY 2 DENSITY : xxx 10 9 PASS SCREEN : xxx An error message is produced if the acquired weights/densities do not meet the following limits: 15 Valid Samples = Sample_1 > Sample_2 > Calibrate Sub-Routine 2 The Solids Specific Gravity sub-routine calculates the 20 specific gravity of the solid material in a sample of dry solids, based on three weighed samples ( plus the Zero step). The sequence of events for the subroutine is as follows: 25 (1) Zero Step (Zero Load-cell) (2) Calibrate (Liquor Density) (3) Sample_l (Dry Solids Weight) (4) Sample_2 (Slurry Density) 30 Both events 1 & 2 use the standard ZERO and CALIBRATE function screens. The current values stored in non volatile memory can be used or the operator can re calculate both values. 35 The operator is prompted for Sample_1 and Sample_2. Pressing the ENTER key after the sample has been placed WO00/12996 PCT/AU99/00703 - 11 on the load-cell will initiate the entry of sample_l, followed by a prompt for Sample_2. Pressing the ENTER key after sample_2 has been placed 5 on the load-cell will initiate the entry of sample_2. After the entry of sample_2, the sub-routine result will be calculated and displayed as: 10 SUB-ROUTINE : 2 SOLIDS WEIGHT : xxx SLURRY DENSITY : xxx SOLIDS SG : xxx 15 An error message is produced if the calculated Solids Specific Gravity does not fall within the following limits: Valid Result = 0.700 <= SOLIDS SPECIFIC GRAVITY <= 20 6.000 Sub-Routine 3 The Variable Volume sub-routine allows the operator to 25 perform the CALC function calculations on a sample volume different to the Volume Set as programmed in the SETUP function. The sequence of events for this sub routine is as follows: 30 1. Sample Volume 2. Sample_1 (Sample Weight) The operator places the sample on the load cell and is prompted to enter the sample volume (ml). When 35 prompted, a default volume (as entered in the SETUP menu) is displayed and the operator may choose to accept the default volume by selecting the ENTER key or WO00/12996 PCT/AU99/00703 - 12 or enter a new value by keying in the new value on the numerical keypad, followed by selecting the ENTER key. Pressing the ENTER key after sample_1 has been placed 5 on the load-cell will initiate the entry of sample_1. After entry of Sample_l, the sub-routine will calculate the following properties of the slurry being tested and display the results of the calculations as: 10 - Slurry Density in grams per litre (gpl) - Slurry percent solids (by weight) - Slurry percent solids (by volume) - Grams solid per litre of slurry(gpl) 15 SETUP Provides access to retained SETUP screens. The setup 20 screens provide the operator with a means of entering the following parameters: (i) Volume Set; 25 (ii) Solids Density; and (iii)Auto Timer Off. The Volume Set parameter defines the volume in ml of 30 the container that holds the slurry being tested for use in subsequent calculations. The Volume Set parameter is retained in non-volatile memory and may be modified by selecting the SETUP key. 35 When selected, the Volume Set screen displays the current setting, the operator may choose to accept the WO00/12996 PCT/AU99/00703 - 13 current value by selecting the ENTER key or may enter a new value by keying in the new value, followed by selecting the ENTER key. 5 The operator is warned if the entered value is not within the valid parameter range - invalid values are not accepted. The Solids Density parameter defines the density in gpl 10 of the dry mineral solids in the slurry being tested. The Solids Density parameter is retained in non volatile memory and may be modified by selecting the SETUP key. 15 When selected, the Solids Density screen displays the current setting, the operator may choose to accept the current value by selecting the ENTER key or may enter a new value by keying in the new value, followed by 20 selecting the ENTER key. The operator is warned if the entered value is not within the valid parameter range - invalid values are not accepted. 25 The Auto Timer Off parameter defines the time the unit will remain online without any keypad entry. The Auto Timer Off parameter is retained in non 30 volatile memory and may be modified by selecting the SET UP key. When selected, the Auto Timer Off screen displays the current setting, the operator may choose to accept the 35 current value by selecting the ENTER key or may enter a new value by keying in the new value, followed by selecting the ENTER key.

WO00/12996 PCT/AU99/00703 - 14 The operator is warned if the entered value is not within the valid parameter range - invalid values are not accepted. 5 In use of the apparatus, an operator enters the Volume Set parameter, the Solids Density parameter, and the Auto Timer Off parameter and then follows the sequence shown in the figure. The sequence illustrates a situation in which the 10 operator decides not to accept the current value of the liquid density parameter and uses the apparatus to calculate the value. The sequence includes the following steps: 15 zero Set The first step is to zero the load cell/strain gauge output for the container that will hold the slurry being tested. 20 When the ZERO key is selected, the ZERO screen appears with the current Zero Set value displayed. The operator may choose to accept the current value by selecting the ENTER key or may calculate a new value by suspending 25 the empty container from the load cell and select the ZERO function key. The new Zero Set value is displayed and the operator selects the ENTER key to save the Zero Set value. 30 Future weighing automatically subtracts the Zero Set value from the measured load cell output. Calibrate 35 This step calculates the density of the liquid in use. This will provide a reference point against which the percentage solids and grams solid per litre of slurry WO00/12996 PCT/AU99/00703 - 15 of a subsequent slurry sample can be determined. When the CAL. key is selected, the Calibrate screen appears with the current Calibrate value displayed. The 5 operator may choose to accept the current value by selecting the ENTER key or may enter a new value by keying in the new value, followed by selecting the ENTER key. If the liquid density is unknown, the Calibrate function can be initiated by selecting the 10 CAL key. To calculate the liquid density, the operator suspends the container full of liquid from the load cell and selects the CAL. function key. The new Calibrate value is calculated and is displayed and the operator selects the ENTER key to save the value as the 15 Liquid Density parameter. Calculate This step calculates and displays the following 20 calculated values from a measured weight of the slurry and the pre-inputted values of volume and specific densities of the liquid and the solids: - Slurry Density (gpl) 25 - Slurry percent solids (by weight) - Slurry percent solids (by volume) - Grams solid per litre of slurry (gpl) The operator suspends a container full of slurry from 30 the load cell and selects the CALC function key. The values of slurry density and the other properties listed above are calculated and displayed. The above-described apparatus is a significant 35 improvement over spring balances. Unlike the spring balances, the apparatus of the WO00/12996 PCT/AU99/00703 - 16 present invention is not limited to the use of a solution of specific gravity of 1.0. The apparatus can be used to directly determine the density of the process liquids and retain this value for ongoing use in its programmed 5 routines and sub-routines for the determination of the above material attributes. In addition, the apparatus is not constrained by the use of water at a specific gravity of 1.000 for the determination of Solids Specific Gravity. 10 Unlike the spring balances - which require an exact volume of 1000 ml of sample for the determination of commonly measured slurry properties and solids specific gravity and subsequent manual calculations to arrive at a result - the balance of the present invention will accept 15 any volume of sample. Furthermore, unlike the spring balances - which require an exact amount of 1000 grams of solids for the determination of solids specific gravity and subsequent 20 manual calculations to arrive at a result - the balance of the present invention will accept any amount of solids and return a precise result for specific gravity in a single operation. This attribute of the present invention makes it easy to deal with broken rock samples which cannot be 25 easily sub-divided to an exact weight. The apparatus of the present invention is both mechanically simple and robust. It has no moving parts. The high resolution load cell is protected from the 30 environment by the unit's corrosion resistant, stainless steel construction. The electronic heart of the unit is protected by an IP65 rated housing and the whole unit is constructed with inherent shock resistance. 35 The accuracy of the apparatus of the present invention is maintained by a simple calibration process balance involving the use of a known weight which maintains WO00/12996 PCT/AU99/00703 - 17 the validity of the load cell output. The balance features a multiple stack output memory which enables the operator to access the full range of the unit's subroutines and then retrieve the generated data by scrolling through the memory 5 stack. This output is preferably displayed on a backlit liquid crystal display (LCD) which eliminates the need for excellent local lighting conditions. Power supply for the unit is available from 10 stepped down 240 / 110 volts AC or from an independent rechargeable 12 volt DC battery. The apparatus of the present invention comprises four principal components: PCB, LCD, load cell and power 15 source. Maintenance of the unit can be carried out by a competent electrician and replacement components are readily available. In summary the key features that distinguish the 20 apparatus of the present invention from the spring balance are that it: (i) is not limited to the use of a liquid of specific gravity of 1.0 for the 25 determination of commonly measured slurry properties; (ii) is not constrained by an exact weight of 1000 g of solid material for the 30 determination of solid specific gravity; (iii) is not constrained by a sample volume of 1000ml of slurry for determination of commonly measured slurry properties; 35 (iv) can use a fixed or variable volume of slurry to calculate the physical properties WO00/12996 PCT/AU99/00703 - 18 of: - Slurry Density (gpl) - Slurry percent solids (by weight) 5 - Slurry percent solids (by volume) - Grams solid per litre of slurry (gpl) - Solids Specific Gravity; (v) offers the capacity to simply determine 10 pulp properties which are not available with the spring balance: - Slurry percent solids (by volume) - Grams solid per litre of slurry (gpl); 15 (vi) is not constrained by the use of water of a specific gravity of 1.000 for the determination of solids specific gravity; 20 (vii) offers subroutines for the determination of: (1) % Passing Screen Size (2) Solid Specific Gravity (SG); 25 (viii)provides a continuous data output over a wide range of material and pulp specific gravities; 30 (ix) is characterised by the superior accuracy of digital technology over mechanical analogue technology; (x) is unaffected by the physical and chemical 35 contaminants commonly present in mineral processing environments; WO00/12996 PCT/AU99/00703 - 19 (xi) is simply and accurately recalibratedT and (xii) has no moving parts. 5 Many modifications may be made to the preferred embodiment described above without departing from the spirit and scope of the present invention.