PH12018050159A1 - Enhanced methods of extracting precious metals - Google Patents

Abstract

This invention provides the extraction of precious metals using an enhanced chlorination process. This is done through a variation of the chlorination process that utilizes chloride to oxidize sulfides, which physically lock the gold components of the ore and allows the dissolution of any gold exposed to the lixiviant. Among the reagents used are sodium hypochlorite (NaOCl), calcium hypochlorite (Ca(OCl)2) and sodium chloride (NaCl).

Description

overflows to second compartment 532 with a cocopeat-zeolite layer for the = second stage of treatment. The treated water from the second stage proceeds to — third compartment 533 with 100% zeolite for the final stage of treatment. The - treated water from the third stage, together with clear water CW, is then = s discharged to river R. ox

The preferred embodiment of this invention is described in the above-mentioned - detailed description. It is understood that those skilled in the art may conceive = modifications and/or variations to the embodiment shown and described therein. =

Any such modifications or variations that fall within the purview of this description = are intended to be included therein as well. Unless specifically noted, it is the ~ intention of the inventors that the words and phrases in the specification and claims be given the ordinary and accustomed meanings to those of ordinary skill in the applicable art. The foregoing description of a preferred embodiment and best mode of the invention known to the applicant at the time of filing the application has been presented and is intended for the purposes of illustration and description. It is not intended to be exhaustive or to limit the present invention to the precise form disclosed, and many modifications and variations are possible in the light of the above teachings.

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ENHANCED METHODS OF EXTRACTING PRECIOUS METALS =

TECHNICAL FIELD OF THE INVENTION -

This invention pertains in general to the extraction of precious minerals and more - s particularly to the extraction of gold using an enhanced chlorination process. i»

BACKGROUND OF THE INVENTION -

Small-scale miners of precious metals like gold in developing countries, because > of lack of sufficient capitalization, often resort to the use of mercury (through LT amalgamation) to extract gold and reprocessed the mine tailings with the use of cyanide (through cyanidation). This method exposes mercury and a possible transformation to methylmercury, an organic mercury which is more lethal.

Methylmercury is a neurotoxin that adversely affects the environment and health of living organisms.

Although cyanidation is an attractive procedure for small-scale miners due to its simplicity and its non-dependence to special equipment, the laborers are inevitably exposed to a chemical that destroys each and every cell it comes in contact to by cell-wall destruction. Studies have pegged that the maximum allowable cyanide exposure for humans is 0.2 ppm in water and 10 ppm in air.

The typical cyanide dosage used in cyanidation is around 2 ppm, which is more than enough to cause adverse effects to the body. Also, when the pH level of cyanide reaches near neutral (cyanidation is conducted at basic conditions), then hydrogen cyanide is formed, which can cause poisoning by inhalation.

Amalgamation, or the recovery of gold by allowing it to form an alloy with mercury called amalgam, is also a method-of-choice by small-scale mining operations.

Using this process, gold is liberated enough to allow mercury to come in contact.

Gold can then be separated from mercury by applying heat to volatilize the low- IS vapor pressure mercury. The gold remaining is then smelted to yield the bouillon. ~

Amalgamation uses about 0.5 Ibs mercury per metric ton of gold ore. However, - the health trade-off of the laborers is also apparent, as the final recovery of gold © s from amalgam requires the mercury to be volatilized. Mercury vapor has long we been deemed as a toxic substance that may cause poisoning should a person be - exposed to vapors at 0.0002mg/m3, or ingest the mercury at 0.002 mg/kg body ~ weight/day. The effects include weakness, respiratory illness, and at higher = levels, even death. -

US5232490A (490) discloses an “Oxidation/reduction process for recovery of » precious metals from MO: ores, sulfidic ores and carbonaceous materials.” discloses a process for separating precious metals from an MqO2, sulfidic or carbonaceous refractory ore or refractory feed such as tailings. The process of ‘490 includes the step of leaching a feed with a leach liquor that includes an acid selected from the group of HCI and H2SO4 in the presence of MiO: and a reductant. A source of chloride ion is added to the leach sufficient to dissolve at least about 50% of the precious metals present in the ore. A portion of the leach is removed and precious metals are recovered from the removed portion. A portion of the chloride carrier is recycled to the leach to carry chloride values to the leach. In one embodiment, HC! is regenerated by pyrohydrolysis, which minimizes harmful waste products. According to ‘490, its process can advantageously avoid the use of noxious reagents. D1 also teaches the processes of gravity concentration, flotation, precipitation and treatment of tailings. Among the objectives of ‘490 is to control the release of cyanide compounds into the environment. However, the process of ‘490 is complicated and therefore costly as it targets primarily big mining companies as its users.

SUMMARY OF THE INVENTION ~

This invention provides a cheaper method of extracting precious metals from ores o without using any mercury or cyanide. This is done through a variation of the = chlorination process that utilizes chloride to oxidize sulfides, which physically lock oe the gold components of the ore and allows the dissolution of any gold exposed to — the lixiviant. -

BRIEF DESCRIPTION OF THE DRAWINGS =

Figure 11s a block diagram of the processes taught by the invention. -

Figure 2 is a diagram of the crushing and grinding process.

Figure 3 is a diagram of the concentration process.

Figure 4 is a diagram of the dewatering process.

Figure 5 is a diagram of the extraction process.

Figure 6 is a diagram of the tailings and wastewater treatment process.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figures 1 to 6, the system is disclosed by this invention comprising of five processes namely crushing and grinding 1, concentration 2, dewatering 3, extraction 4, and tailings and wastewater treatment 5.

G) In crushing and grinding process 1, the ore undergoes size reduction. The ore is received and goes to a jaw crusher 10 and the product through belt conveyor 11.

Any oversized ore (coarser than 1/2 inch) from a screen 12 goes to a roll crusher 13, while the undersized (finer than 1/2 inch) ore goes to a fine ore bin 14. The crushed ore with water are then fed into a ball mill 15 to achieve a product size with 80% passing 75 um. The product is then pumped to a hydrocyclone 16. The underflow (coarser than 75 um) is recycled back to ball mill 15 while the overflow — (75 um and finer) flows to a Falcon feed tank 17. =

Falcon feed tank 17 feeds a Falcon gravity concentrator 21. Concentration in the on

Falcon takes about 30 minutes per cycle (approximately 1 MT per cycle). The - concentrate that contains the free gold is then collected in buckets. After which, - the concentrate is fed to a table concentrator 22 for further cleaning. Table 22 = produces a cleaner gold concentrate G, which is collected by a customized = vacuum (not shown). The tailings GCT from Falcon gravity concentrator 21 and = table 22 go to a flotation feed thickener 23. The pulp from flotation feed thickener 23 is pumped to a flotation feed conditioning tank 24. The pulp is mixed thoroughly inside conditioning tank 24 and the percentage of solids is maintained at 40%. The pH is adjusted to pH 9 with the addition of lime. The reagents used are CMS, a thionocarbamate collector, and Interfroth (IF) 6500, a glycol-based frother. A 10 gpt dosage of CMS and a 50 gpt dosage of IF6500 were used. After a total of 30 minutes conditioning time, the pulp is fed to rougher- cells 25a. The rougher concentrate RC flows to cleaner cells 26 while the rougher tails go to scavenger cells 25h. The scavenger concentrate SC is also fed to cleaner cells 26. The cleaner concentrate is pumped to the re-cleaner 27 for further cleaning.

The re-cleaner concentrate contains the gold associated and/or locked in sulfide minerals and becomes the final flotation concentrate FFC. The cleaner tails and re-cleaner tails RCT is recycled back to rougher cells 25a. On the other hand, the cleaner tails and scavenger tails become the final flotation tails FFT and go to final tails thickener 28.

The extraction of metallurgy employs a simultaneous oxidation and leaching processes. Oxidation is necessary to convert the sulfide minerals to oxide before leaching. A mixture of solution containing sodium hypochloride, calcium hypochloride, sodium chloride and sodium hydroxide is first fed into the oxidation/leaching tank 42. The solution is mixed thoroughly to achieve = homogeneity before adding final flotation concentrate FFC and shaking table oo concentrate. After 1.5 hours, calcium hypochloride is added. After 3 hours, pH is ” adjusted to pH 9 using hydrochloric acid. When the desired pH is achieved, = calcium hypochloride is again added. The addition of calcium hypochloride is - done every 10 minutes until the 4th hour. After the 4th hour, oxidation/leaching - tank 42 is emptied. The mixture goes to filter press 32 for dewatering. The ~ pregnant solution PS that contains the leached gold is collected in precipitation - container 44 via a launder (not shown). Gas coming from the oxidation/leaching = tank 42 is processed inside a gas scrubber 43 where it is treated and clean air is = released as a result. Sodium chloride is a by-product of scrubber 43.

The extraction process for gold employed is a 2-stage chlorination process. The or process uses calcium hypochlorite as the hypochlorite-bearing reagent, sodium chloride to stabilize the gold-chloride complex, and caustic soda and hydrochloric acid as pH-modifying reagents. The first stage is a 3 - 4 hours oxidation stage wherein the sulfides minerals in the flotation concentrate is oxidized in alkaline conditions. The pH is adjusted to 9.5 at the start and it is monitored throughout the oxidation process. Caustic soda is added to maintain the pH to 9.5. In this stage, partial dissolution of exposed gold already occurs. Following the first stage is the second stage where the gold exposed from the oxidation stage is actively dissolved in neutral pH conditions. Here, the pH is adjusted and maintained around the range of 5-7 for 4 hours, with weighed amounts of calcium hypochlorite being added at 10-15 minute intervals.

The employed extraction process was optimized through a variation of the chlorination process. As its name entails, the chlorination process utilizes chloride to oxidize sulfides which physically lock the gold components of ore and it also allows the dissolution of any gold exposed to the lixiviant. In this modified chlorination protocol, the main reagents are sodium hypochlorite, calcium - hypochlorite and sodium chloride. In addition, sodium hydroxide and hydrochloric - acid are used as pH modifiers. Table 1 shows the percent volume of each - extraction reagent with respect to the lixiviant volume. = i.

Table 1 - Percent Volume of Reagents - oo | ws] =

The developed process that accounts for the fast production of sulfuric acid without sacrificing the efficiency in dissolving gold through a 2-stage leaching process is performed. The first stage is leaching at alkaline conditions for three hours in order to partially oxidize most of the sulfides while preventing any drastic changes in the pH due to the sulfuric acid product of the oxidation reaction. This is done by mixing the main reagents for five minutes. Thereafter, 100g of the flotation concentrate is added to the solution. The second stage involves the leaching of the gold exposed from the previous oxidation process and the rest of the free and exposed gold prior to the leaching process. After the first stage, a small amount of hydrochloric acid is added to lower the pH. Fixed amounts of calcium hypochlorite are added at time intervals for the whole second stage in order to replenish the amount of lixiviant consumed in the first stage. The mixture is then filtered.

After the extraction process, the aqueous solution that contains the dissolved - gold is separated from the solid residue and it will undergo the precipitation - process to recover the gold. ~

To precipitate the gold, sodium metabisulfite is added in precipitation container o 44. The solution is mixed thoroughly for at least 5 minutes. Thereafter, ascorbic acid is also added. The solution is again mixed thoroughly for at least 5 minutes. -

The solution is left for about 2 hours to precipitate the gold. The solution is then - filtered using pressure filter 45 to separate gold precipitates GP. o

The gold precipitates GP is mixed with borax and undergo refining using a blow - torch to produce the final product — a gold bead.

The tailings from final tails thickener 28 is discharged into final tailings settling pond 51. The solids are allowed to settle producing clear water CW that can be disposed to a natural body of water like river R. The solids from final tailings settling pond 51 and the barren solids BS from filter press 32 and pressure filter 45 can be packed into sacks 56 or similar containers for final disposal or may be utilized as additional support structures to counter erosion or even for landscaping.

The washings and barren solution (considered as the wastewater from pressure filter 45) are placed in neutralization tank 52 to neutralize the pH using sodium hydroxide before discharging to the wastewater treatment compartment 53.

The neutralized barren solution is then discharged from wastewater treatment's 53 first compartment 531. The solution then flows through cocopeat — zeolite layer 54. The treated water at the bottom of cocopeat-zeolite layer 54 goes to a holding area/empty compartment 55. When this compartment becomes full, it

Claims (1)

1. CLAIMS - oY 1. A method for extracting precious minerals comprising the steps of: O

   A. crushing an grinding of ore; i

   B. concentrating the crushed ore;

   C. dewatering of the concentrate; -

   D. extracting the precious metals from the concentrate; and / -

   E. treating the tailings and wastewater. -

   2. The method according to claim 1 wherein Step D comprises a chlorination ~ process using hypochlorite solutions for leaching.

   3. The method according to claim 2 wherein the main reagents comprises sodium hypochlorite (NaOCl), calcium hypochlorite (Ca(OCl)2) and sodium chloride (NaCl) and(the)pH modifiers comprises sodium hydroxide and hydrochloric acid. v

   5. The method according to claim 3 wherein the percent volume of NaOCl with respect to a lixiviant volume is 50%-80%. S00 gpl. 12 2 [patty A 109

   6. The method according to claim 3 wherein the percent volume of Ca(OCl). C with respect to@)ixiviant volume is 6-10%.

   7. The method according to claim 3 wherein the percent volume of NaCl with respect to(@)lixiviant volume is 10-30%. ~

   8. The method according to claim 3 wherein the percent volume of NaOH with respect to(@)ixiviant volume is 0.5-2%. C 17 9-2 aod wey

   9. The method according to claim 3 wherein the percent volume of HCI with C respect to(alixiviant volume is 1-5%. -

   10. The method according to claim 3 wherein the main reagents and the pH = modifiers have the following optimal percentage volume to a lixiviant: oo pot : Ca(OCl, ne - . ;

   11. The method according to claim 3 wherein the leaching process comprises two °."- 15 stages.

   12. The method according to claim 11 wherein the first stage comprises leaching at alkaline conditions for three hours following the steps of:

   A. mixing the main reagents for five minutes; and 20 B. adding a 100g of the flotation concentrate to the solution.

   13. The method according to claim 11 wherein the second stage comprises aching of the gold exposed from the previous oxidation process and the rest of the free and exposed gold prior to the leaching process following the steps of: 25 A. adding a small amount of hydrochloric acid to lower the pH;

   B. adding fixed amounts of calcium hypochlorite at time intervals to replenish the amount of lixiviant consumed in the first stage; and

   C. filtering the mixture for the precious metal content.