AU2003252756B2 - Chemical formulations and methods for treating self-heating metal ores - Google Patents

Description

P/00/011 Regulation 3.2 AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention Title: CHEMICAL FORMULATIONS AND METHODS FOR TREATING SELF-HEATING METAL ORES Applicant: APPLIED CHEMICALS PTY LTD The following statement is a full description of this invention, including the best method of performing it known to me: 2 CHEMICAL FORMULATIONS AND METHODS FOR TREATING SELF-HEATING METAL ORES 5 Field of the Invention This invention relates to the treatment of metal ores prone to self heating. More particularly the invention provides chemical formulations and methods of application of such formulations to metal ores to prevent or at least 10 reduce the risk of, or extent to which such ores undergo, self-heating. Background When mined, metal containing ores generally exist as part of a mixture of 15 material, including both a variety of different metal-containing ores and unwanted contaminants such as soil, rock and organic matter. Once removed from the ground the mined material is generally processed to remove unwanted contaminants and the various metal-containing ores are separated, prior to being transported to a processing plant, for further processing such as smelting. 20 The removal of the unwanted contaminants is normally done by some sort of washing process. In some mines, after washing the cleaned ore is dried and then transported in that dried state. In others, the washed ore is formed into a slurry and the slurry pumped to a processing plant, such as for example a 25 drier or filter press. It is not unusual for such slurries to be pumped large distances of up to several hundred kilometres or more. The slurry will then be dried prior to further processing. Typically the clean dried ore is stockpiled at some point prior to being 30 processed. This includes stockpiling at the mine site before being transported, such as for example by truck or ship. In those cases where slurries are transported by conveyor, the ores will be stockpiled after drying at a site remote from the mine. W:\Megan\NB\NODELETE\Specifications\IRN 704595.doc 3 In their natural state most metal ores exist usually as sulphide salts, although other forms, such as for example carbonates, are also often present. The cleaned metal sulphide ores are known on occasion to 5 spontaneously react generating substantial amounts of heat. The mechanism of self-heating is not fully understood, but is thought to occur through the generation of heat when dry ore comes into contact with moisture. This heat of hydration is thought to cause the sulphide to convert to both sulphur dioxide and the metal sulphate. In extreme cases the metal salt fuses and melts to form a 10 solid mass of metal. Self-heating is known to occur with many metal ores including in particular zinc, copper, nickel and lead. The self-heating of metal sulphide ores is a substantial concern to the mining industry. The sulphur dioxide produced is highly toxic. Furthermore, the 15 metal sulphates created can cause difficulties during smelting. Left untreated hotspots can form deep inside stockpiles, which can lead to reactions of extremely high temperatures. Base metal salts can become so hot that the ores containing them commence smelting in stockpiles or during 20 transport. This problem is particularly acute where the ore is held in a confined space such as typically occurs when being transported by ship. The heat generated by shipped ores can lead to high temperature reactions fires in the ship which put the ship at risk. On occasion high temperature reactions fires from shipped ores have necessitated the dumping of the entire ore load 25 overboard. Current methods of controlling the problem of self-heating in the main revolve around mechanical methods. 30 Where ore is stored in stockpiles of less than a critical size, the rate of heat dissipation will be greater than or equal to the heat generated by the reacting ore. Although in such cases these stockpiles are unlikely to reach critical temperatures, formation of unwanted metal sulphates still can occur. Moreover, the critical size of such stockpiles is small and the process of W:\Megan\MNB\NODELETE\Specifications\RN 704595.doc 4 maintaining the ore in such small amounts is largely impractical and uneconomical. An alternative to maintaining small stockpiles involves careful control of 5 the particle size of the ore itself. Reduction of the size of the individual ore particles also results in a reduction in the amount of air movement through the stockpile, thereby lowering or minimizing the moisture loss and thus stabilizing the temperature of the ore. However, adequate particle size control is difficult to achieve and is also expensive. In practice it is difficult to ensure a uniform 10 particle size throughout a body of ore and it is often the case that there will be sites of various sized particles within a stockpile. In such cases there is a high risk of a spontaneous self-heating cycle commencing at these sites. In a generally low particle size stockpile, this can provide an environment that is highly insulated from heat-loss. Consequently, self-heating in such stockpiles 15 can result in even more catastrophic loss of sulphide ore than in stockpiles of larger particle size. Other alternative methods of dealing with the problem of self-heating ores have included attempts to control the moisture level of the ore body. 20 Whilst, as noted above, heat is thought to be generated by hydration of dry ore, the heat generated will be dissipated where a sufficient amount of water is present. Therefore, methods used in the past have included spraying of stockpiles with water and managing stockpiles such that the moisture in the stockpile is maintained above a certain critical level prior to processing. Such 25 methods have largely been ineffective. Generally, high moisture content is to be avoided as it renders the ore difficult to handle. It also renders the ore unsuitable for transport particularly by ship. Inevitably during transport by ship the ore will be subjected to vibration, 30 caused, at least in part by the ship's engines. Vibration of a wet ore body tends to cause slurries to form. Such slurries can seriously upset the stability of ships transporting ores, particularly in rough seas. Slurries also provide difficulties during unloading of the ore. W:\Megan\MNB\NODELETE\Specifitions\RN 704595.doc 5 Usually, moisture levels of between about 11 and 12% w/w are optimal for both handling and transport of ores. At levels below about 11 % w/w the ores tend to be dusty, whilst at levels above about 12% w/w there is a substantial risk of slurries forming, particularly during transport. 5 The maintenance of moistures levels within the preferred 11 to 12% w/w range is difficult to achieve. Generally, ore is stockpiled for about seven weeks prior to transport and natural loss of moisture content will usually be rapid and substantial. It is not exceptional for moisture levels within a stockpile to drop 10 from about 12% to about 9% w/w within one week. Furthermore once the moisture content in an ore body drops below about 9% w/w, the ore particles become extremely hydrophobic and difficult to re-wet. Metal sulphide ores in particular are known to be difficult to re-wet when they reach a low moisture level and consequently the addition of further water such as by water sprays are 15 of little effect in such cases. Summary of the Invention In one aspect of the present invention there is provided a chemical 20 formulation for application to metal sulphide ore to reduce its propensity to spontaneously self-heat, wherein the formulation includes: (a) low foaming surfactant component; (b) alcohol or alcohol derived component; 25 (c) wetting agent component. A further aspect of the present invention provides a method of treatment of ore, including the application of the formulation to the ore. 30 Detailed Description The Formulation In one aspect the chemical formulation of the present invention includes: 35 W:\egan\NB\NODELETE\Specifications\RN 704595.doc 6 (a) low foaming surfactant component; (b) alcohol or alcohol derived component; (c) wetting agent component. 5 The low foaming surfactant provides a film which forms on the ore particles. Such filming reduces the amount of oxygen able to react with the metal in the particle and also helps retain moisture. The low foaming surfactant component of the formulation includes 10 carboxylic acids and/or derivatives thereof, including esters, amides (including alkanolamides) and salts and mixtures thereof. Suitable carboxylic acids include long, medium and/or short chain carboxylic acids, including mono, dimer or trimer acids. Preferably they will be 15 of from C4 to C18, more preferably C4 to C12 carbon chain lengths, either straight chain or branched. They may be derived from any suitable source, including natural (vegetable), synthetic (manufactured from other organic chemicals) or hydrocarbon (petroleum refinery feed stock). Preferably the esters are derived from carboxylic acids having little or no degree of unsaturation. Suitable esters 20 include those derived from such carboxylic acids esterified with triethanolamine, diethanolamine or dimethyl amino ethanol. Preferably the formulation includes a mixture of suitable carboxylic acids and esters in a ratio of between 10:90 to 30:70 w/w. Examples of suitable 25 commercially available ester/acid mixtures are Alox 232 and Megalox 4232 (Alox Corporation). The low foaming surfactant component of the formulation preferably includes one or more fatty acids and salts thereof, preferably amine salts. 30 These may be included in carboxylic acid/ester mixtures such as are referred to above, or may be additional to such mixtures. The fatty acid assists the formation of the film and also assists in neutralizing the charges on the surface of the ore particles. Suitable fatty acids include saturated and unsaturated fatty acids and salts thereof, preferably having from C12 to C18 chain lengths. It is W:\Megan\MNB\NODELETE\Specifications\RN 704595.doc 7 also preferred that the one or more fatty acids has a low rosin acid content. Most preferred is a rosin acid level of below 30 parts. Oleic acid is preferred. It is preferred that the formulation includes from about 1 to about 20 parts 5 of the low foaming surfactant component. Of this about 1 to about 20 parts, the low foaming surfactant component preferably includes from about 1 to about 10 parts, more preferably from about 3 to about 5 parts carboxylic acid esters, 1 to 10 parts carboxylic acid salts, more preferably from about 0.1 to about 1 part C4 to C12 carboxylic acid amine salts and from about 1 to about 8 parts C18 mono 10 unsaturated carboxylic acid amine salts. The formulation includes an alcohol or alcohol derived component. This component may include alcohols or derivatives thereof including alkanols, alkylene glycols, alkylene glycol ethers including mono and di alkyl ethers and 15 polyalkylene glycols and mono and di ethers thereof. Preferably, this component includes C2 and C3 alkylene glycols mono and di ethers of C1 to C6 alkyl ethers, polyalkylene glycols containing from 2 to 10 alkylene glycol units and mono and di ethers thereof formed with C1 to C6 alkyl ethers, more preferably C2 and C3 alkylene glycols and mono and di (C1 to C6) ether and 20 diethylene glycol. Most preferred are ethylene, propylene, diethylene, dipropylene and hexylene glycols, and diethylene glycols, mono and diethyl ether, ethylene glycol monobutyl ether and diethylene glycol mono and dibutyl ether. 25 It is preferred that the formulation includes from about 1 to about 20 parts of the alcohol or alcohol derived component. Of this is preferably included about 1 to about 10, preferably about 2 to about 8, more preferably about 5 to about 7 parts straight chain mono alcohol and about 1 to about 10 preferably about 2 to about 8, more preferably about 6 to about 8 parts polyglycols or 30 alcohol ethers, or more preferably glycol ethers and diethers derived from dihydric alcohols. The formulation also includes one or more wetting agents. Suitable wetting agents include any that are relatively high wetting at low concentrations, W:\Megan\MNB\NODELETE\Specifications\IRN 704595.doc 8 such as for example sulfonate based surfactants, preferably olefin based sulfonates, more preferably sulfosuccinates, such as sodium dioctyl sulfosuccinate; sodium n-lauroyl sarcosinate, cocoamido betaines, and sodium lauryl ether sulphates among others. Sodium dioctyl sulfosuccinate is 5 particularly preferred. Preferably the formulation includes from about 0.1 to about 5 parts w/w wetting agent, more preferably from about 0.1 to 3 parts, more preferably about 0.2 to 2 parts. 10 The formulation also preferably includes one or more alkanolamines. Suitable alkanolamines include monoethanolamine, diethanolamine and triethanolamine, among others. It is preferable that sufficient alkanolamine is included to result in the formulation having a pH of between about 7 and about 15 9, more preferably about 8. Preferably the formulation includes: (a) from about 1 to about 20 parts, more preferably 5 to 10 parts, 20 more preferably about 7 to 8 parts low foaming surfactant; (b) from about 1 to about 20 parts, more preferably 4 to 16, more preferably 10 to 15 parts alcohol or alcohol derived component; (c) from about 0.1 to 5, preferably 0.1 to 3, more preferably 0.2 to 2 parts of wetting agent. 25 Particularly preferred formulations can be prepared having the following composition: (a) C4 to C12 carboxylic acid esters 3 to 5 parts 30 (b) C4 to C12 carboxylic acid 0.1 to 0.5 parts; (c) C18 monounsaturated fatty acids 3 to 5 parts; (d) Propylene glycol 2 to 8 parts; (e) Ethanol or isopropyl alcohol 2 to 8 parts; (f) Triethanolamine 1 to 4 parts; W:\Megan\MNB\NODELETE\Specifications\RN 704595.doc 9 (g) Sodium dioctyl sulfosuccinate 0.1 to 3 parts; and (h) Water to 100 parts. Another preferred formulation is: 5 (a) C4 to C12 carboxylic ester of dimethyl aminoethanol 4 parts; (b) C4 to C12 carboxylic acids 0.4 parts; (c) C1 monounsaturated fatty acids 3.5 parts; (d) Ethyl alcohol 6.5 parts; (e) Sodium dioctyl sulfosuccinate 0.5 parts; 10 (f) Propylene glycol 7.5 parts; (g) Triethanolamine 3 parts; and (h) Water to 100 parts. The above discussion of the formulation, including the preferred amounts 15 of particular constituents, is in terms of a base formulation or concentrate. In use this concentrate will generally be diluted in water by factor of between about 10 and 100 v/v. In this specification a reference to "parts" is by weight. 20 Example 1 Formulation made up of the following components was prepared as described below under Method of Preparation. 25 Component Parts Weight " Triethanolamine 3.0 " Ester/carboxylic acid mixture 30 - Alox 232 2.0 - Megalox 4232 2.0 * Oleic Acid - Priolene 697 3.5 e Sodium di-octyl sulfosuccinate - Fedwet 302 0.5 35 0 Ethanol AlcoFlex 95 6.5 e Propylene Glycol 7.5 e Water 75.0 W:\Megan\MNB\NODELETE\Specifications\IRN 704595.doc 10 Method of Preparation The formulation ca be prepared using the following procedure. 5 1. In a clean stainless steel vessel add water, glycol and alcohol and commence stirring. 2. Add the sodium di-octyl sulfosuccinate, carboxylic acid ester (Alox 232 and Megalox 4232) and fatty acid (Priolene 697) and stir for 15 minutes. 3. Add the Triethanolamine and stir until clear (approximately 10 10 minutes). 4. Adjust pH using small increments of fatty acid or Triethanolamine as appropriate to bring the pH to about 8. 5. Once desired pH achieved, put into containers to avoid oxidation. 15 The Method of Treatment The method of treatment of metal ores comprises the application of the formulation to ore so as to coat or partially coat individual ore particles. 20 Any suitable method of application of the formulation to the ore may be used. Figure 1 shows a schematic diagram of a typical process of a metal ore from extraction from a mine to production of refined smelted metal, such as zinc sulphide. As can be seen from Figure 1, in such a process after extraction from the mine the ore is crushed and washed and separated to form a slurry. The 25 slurry is then pumped to a drying plant and then on to a thickener (where the slurry is settled from its water carrier in a large holding tank). The thickened ore then proceeds to a filter press and onto a drier pelletizer before being stockpiled. The clean dried ore is then transported to a smelter for smelting. 30 The formulation of the invention may be applied to the ore at any suitable point along this production line. As shown in Figure 1 these include at positions marked (1) to (4). (1) One suitable point for the application of the formulation is after the 35 ore has been stockpiled following drying and pelletizing. Ore is often held in a W:\Megan\MNB\NODELETE\Specifications\RN 704595.doc 11 temporary stockpile before being transported to a smelting site. Movement from the initial stockpile will often be by conveyor. In such cases the formulation can be applied to the dry ore as the ore moves along a conveyor system. Figure 2 is a schematic drawing of one example of a suitable application system. 5 As shown in Figure 2A, ore is conveyed along a first upper conveyor belt (usually in the order of 800-1200 mm wide) and projected from the end of that conveyor down against a rubber splashback before falling onto a second lower conveyor. Diluted formulation is sprayed into the ore from above and below the 10 ore stream as it travels from the end of the first upper conveyor to the splashback. A series of jets as shown in Figures 2A and 2B direct the formulation so as to obtain optimal coverage. Diluted formulation is sprayed onto the ore through a fixed spray boom, 15 where spray nozzles are arranged both above and below the ore flow, and are angled such that the spray pattern covers the entire surface of the ore body. The position, size and volume of the spray system used is designed to permit adequate diluted formulation to contact the ore during the highly turbulent mixing action against the splashback. Care is required to ensure that excessive 20 fluid is not applied, as this may result in the ore body becoming wet and clump, preventing mixing. Thorough mixing and intimate particle/fluid contact is required at these points, as no mixing occurs during movement along transports systems such as conveyors. If the correct pattern, volume and spray pressure are achieved, then with the turbulence obtained at the splashback and the film 25 forming capacity of the formulation, effective coating of the ore particles occurs within the confines of the application area. Figures 2A and 2B show a spray assembly consisting of four upper nozzles on a spray bar above the ore flow and two lower nozzles on a bar 30 below. This spray assembly provides good coverage of the ore body. The upper nozzles consist of two 40* V jets in the centre, which direct formulation onto the top surface of the ore body and two 30* V jets, one on each side of the top spray bar, which direct formulation to the sides of the ore body. In this W:\Megan\MNB\NODELETE\Specifications\IRN 704595.doc 12 arrangement, the nozzles are configured such that their respective spray patterns overlap by approximately 15 parts. The lower nozzles consist of two 300 V jets in the centre of the bar, 5 configured such that their spray pattern covers the entire under surface of the ore body and overlap by approximately 25 parts. For this type of spray configuration, spray pressures are preferably between about 300 and 600 KPA with the upper 400 V jets delivering approximately 16 litre/min and the 30* V jets (both upper and lower) delivering approximately 12 litre/min at a pressure of 10 approximately 300 KPA. The number and configuration of spray jets may be varied as appropriate, depending on the conveyor system used. For example where a relatively narrow conveyor is used the 400 and 300 jets described above may be 15 replaced by 300 and 200 respectively jets. In such a case the 200 jets should have the capacity to deliver about 8 litres of diluted formulation per minute, running at a pressure of 300 KPA. (2.) In an alternative method the diluted formulation can also be applied to 20 the ore as the ore exits the drier, prior to being stockpiled in a reclaimer shed, for example. As the ore body exits the drier, it undergoes turbulent mixing in the same manner described above in (1), in a splashback arrangement as described above. Immediately following drying, the surface oxidisation of the ore pellets or particles is at or near its minimum level. Also moisture levels are 25 generally at or between about 12% w/w and about 14% w/w which provide near to or optimum levels to allow for effective spreading of the formulation over the surface of the ore particles. (3.) In a further alternative process the formulation can be applied to a wet 30 slurry such as is described above in relation to Figure 1. In an example of such a process the formulation is added to the wet slurry in the thickener tank or prior to filter pressing and entry to the dryer. An advantage of such a process is that the level of contact between the ore particles and the formulation is greater than typically occurs in spray applications to dry ores, such as in the processes W:\egan\MNB\NODELETE\Specification\IRN 704595.doc 13 previously described. However, the level of fluid film on the particles tends to be correspondingly lower. A further advantage of this type of process is that it comprises the agglomeration of ore particles, resulting in an improved concentration performance. The formulation is preferably added to the slurry at 5 the point the slurry enters the thickener tank. An application rate of about 100 ppm formulation to slurry (10 gram formulation per 100 litres slurry) is suitable. The application can be made by use of a simple electronic proportional dosing pump, such as is capable of a delivery rate of between about 20 and 150 millilitres formulation per minute. Where the formulation is applied to a slurry 10 such as in this type of method, a further additional low level of formulation may be applied to the ore upon exit from the dryer. This may be appropriate to improve surface film builds, particularly for highly reactive ores (such as those with a higher surface charge than zinc sulphide, for example). Suitable dose rates for such processes are from about 50 to about 100 ppm (g of formulation 15 per dry weight ore). (4.) In a further alternative process formulation can be added to wet ore after it has left the thickener tank but before it enters the filter press. Application of the formulation in such a process can be by a spray system such as previously 20 described in (1) and (2) above. With this process the formulation is applied to the ore slurry at the exit point of the thickener tank, where the ore concentration is about 50 parts w/w in water. This method provides excellent fluid/particle contact when surface moisture is at its maximum and also allows high fluid surface film builds. In this case the formulation contacts the ore slurry when it is 25 in a semi solid form, thus all the formulation attaches itself to the ore. This is different from the thickener application where the formulation is dissolved in water carrying low levels of ore at a much higher concentration than occurs when the formulation is dissolved in water carrying low levels of ore. In this process a very even coating of formulation is able to be achieved. 30 In this specification, a reference to "ore" includes material containing such ore. W:\egan\MNB\NODELETE\Specifications\IRN 704595.doc 14 The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the spirit and scope of the present disclosure. UAPAST STAFF\MEGAN\MNB\NODELETE\SpedficationsuRN 704595.doc

Claims (20)

1. A chemical formulation for application to metal sulphide ore to reduce its propensity to spontaneously self-heat, including: 5 (a) low foaming surfactant component; (b) alcohol or alcohol derived component; (c) wetting agent component. 10

2. A chemical formulation according to claim 1, including: (a) from about 1 to about 20 parts low foaming surfactant; (b) from about 1 to about 20 parts alcohol or alcohol derived component; and 15 (c) from about 0.1 to about 5 parts wetting agent component.

3. A chemical formulation according to either claim 1 or 2 including more than 5 but less than 10 parts low foaming surfactant and wherein the low foaming surfactant component includes one or more carboxylic acid esters 20 including carboxylic acid esters having chain lengths of from C4 to C12.

4. A chemical formulation according to any one of the preceding claims having more than 10 but less than 15 parts alcohol or alcohol derived component. 25

5. A chemical formulation according to any one of the preceding claims having from 0.2 to 2 parts wetting agent component.

6. A chemical formulation according to any one of the preceding claims 30 wherein the low foaming surfactant component includes one or more carboxylic acids including carboxylic acids having chain lengths of from C4 to C12. 16

7. A chemical formulation according to any one of the preceding claims wherein the low foaming surfactant component includes a mixture of carboxylic acids and carboxylic acid esters in a ratio of between 10:90 to 30:70 w/w. 5

8. A chemical formulation according to any one of the preceding claims wherein the alcohol or alcohol derived component includes one or more of methanol, ethanol and propyl and isopropyl alcohol.

9. A chemical formulation according to any one of the preceding claims 10 wherein the alcohol or alcohol derived component includes one or more glycols or glycol ethers.

10. A chemical formulation according to any one of the preceding claims wherein the alcohol or alcohol derived component includes one or more of 15 ethylene, diethylene, propylene, dipropylene and hexylene glycol.

11. A chemical formulation according to any one of the preceding claims wherein the wetting agent includes a sulphonate based surfactant. 20

12. A chemical formulation according to claim 11 wherein the wetting agent includes an olefin based sulphonate.

13. A chemical formulation according to any one of claims 1 to 10 wherein the wetting agent includes sodium di-octyl sulfosuccinate, sodium lauryl 25 sarcoccinate, cocoamido betaines or sodium lauryl ethyl sulphate.

14. A chemical formulation according to any one of the preceding claims further including one or more alkanolamines. 30

15. A chemical formulation according to any one of the preceding claims wherein the formulation includes one or more fatty acids having chain lengths of from c 1 2 to C18. 17

16. A chemical formulation for application to metal sulphide ore to reduce its propensity to spontaneous self-heat including: (a) 3 to 5 parts C4 to C12 carboxylic acid esters; 5 (b) 0.1 to 0.5 parts C4 to C12 carboxylic acid; (c) 3 to 5 parts C18 monounsaturated fatty acids; (d) 2 to 8 parts propylene glycol; (e) 2 to 8 parts ethanol or isopropyl alcohol; (f) 1 to 4 parts triethanolamine; 10 (g) 0.1 to 3 parts sodium dioctyl sulfoccinate; and (h) Water to 100 parts.

17. A method of treatment of metal ore including the application of a formulation according to any one of the preceding claims to metal sulphide ore. 15

18. A method according to claim 17 wherein the application includes spraying the formulation on the ore whilst said ore is being carried by a conveyor system. 20

19. A method according to claim 17 wherein the formulation is added to an ore containing slurry.

20. A chemical formulation substantially as described herein with reference to the example.