WO2019194687A1

WO2019194687A1 - Enhanced methods of extracting precious metals

Info

Publication number: WO2019194687A1
Application number: PCT/PH2019/000003
Authority: WO
Inventors: Herman D. MENDOZA
Original assignee: University Of The Philippines Diliman
Priority date: 2018-04-04
Filing date: 2019-04-03
Publication date: 2019-10-10
Also published as: PH12018050159A1

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

ENHANCED METHODS OF EXTRACTING PRECIOUS METALS

TECHNICAL FIHD OF THE INVENTION

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

BACKGROUND OF THE INVENTION

Small-scale miners of precious metals Kke gold in developfog countries, because of lack of sufficient capitalization, often resort to the use of mercury (through amalgamation) to «(tract gold and reprocessed the mine taings wlh the use of cyanide (through cyanidation). This method exposes mercury and a possible transformation to methybnercury, an organic mercury which is more lethal Methytmercury is a neurotoxin that adversely affects the environment and health of iving organisms.

Although cyanidation is an attiacthre procedure for smaB-scaie miners due to is simplicity and its non-dependence to special equipment the laborers are inevitably exposed to a chemical that destroys each and every cel I 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 fire body. Also, when the pH level of cyanide reaches near neutral (cyanidation is conducted at basic conditions), then hydrogen cyanide is formed, which can case poisoning by inhalation.

Amalgamation, or the recovery of gold by alowing it to form an aloy with mercury caled amalgam, is also a method-of-choice by smafl-scale mining operations. Using this process, gold is Rierated enough to allow mercury to come in contact Gold can then be separated from mercury by applying heat to volatilize the low- vapor pressure mercury. The gold remaining is then smefted to yield the bouton. Amalgamation uses about 0.5 lbs mercury per metric ton of gold ore. However, the heefth trade-off of Die laborers is also apparent, as the ffoal recovery of gold from amalgam requires the mercury to be volatilized. Mercury vapor has long been deemed as a toxic substanoe 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 Iness, and at higher levels, even death. US523249QA (‘490) discloses an“Oxidation/reduction process for recovery of precious metals from

ores, sutikfic ores and carbonaceous materials.” discloses a process for separating precious metals from an MiCk, suifidic or carbonaceous refractory ore or refractory feed such as tafeigs. The process of ‘490 includes the step of leaching a feed with a leach liquor that includes an acid selected from the group of HCt and l-feSQ* in tie presence of Mp(½ and a reductant A source of chloride ion is added to the leach sufficient to dissolve at least abort 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, HCi is regenerated by pyrohydralysis, which minimizes harmful waste products. According to ‘490, its process can advantageously amid the use of noxious reagents. D1 also teaches the processes of gravity concentration, flotation, precipitation and treatment of taifings. 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 ¾ targets primarily big mining companies as fe users. SUMMARY OF THE INVENTION

This invention provides a cheaper method of extracting precious metals from ores 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 the gold components of the ore and atows the dfesolufion of any gold exposed to the lixhrianl

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a block cfiagram 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 compris g of five processes namely crushing and grinding 1, concentration 2, dewatering 3, extraction 4, and taiings and wastewater treatment 5.

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 beft 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

with 80% passing 75 . The product is then pumped to a hydrocydone 16. The underflow (coarser than 75 pm) is recycled back to ban mil 15 while the overflow (75 pm and finer) flows to a Falcon feed tank 17.

Falcon feed tank 17 feeds a Falcon gravity concentrator 21. Concentration in the 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 tor further cleaning. Table 22 produces a cleaner gold concentrate G, which is cofected 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 ptdp from flotation feed thickener 23 is pumped to a flotation feed conrfitioning 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 adkfition of lime. The reagents used are CMS, a thionocarbamate collector, and Interfroth (IF) 6500, a glycol-based frother. A 10 gpt dosage of CMS aid 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 cefls 26 while the rougher tais go to scavenger cells 25b. The scavenger concentrate SC is also fed to cleaner cells 26. The cleaner concentrate is pumped to the re-cteaner 27 for further cleaning. The re-cleaner concentrate contains the gold associated and/or locked in sulfide miierais ana necomes me mai notation concentrate rr . i ne cleaner tais ana re-cleaner tails RCT is recycled back to rougher cells 25a. On toe other hand, toe cleaner tails and scavenger fails become toe final flotation tails FFT and go to final tails thickener 28.

The extraction of metaHisgy employs a siim&aneous oxidation and leaching processes. Oxidation is necessary to convert the suffkte minerals to oxide before leaching. A mixture of solution containing sodium hypochtoride, calcium hypochloride, sodium chloride and sodium hydroxide is first fed into toe oxidation/!eaching tank 42. The solution is mixed thoroughly to achieve homogeneity before adding final flotation concentrate FFC and shaking table concentrate. After 1.5 hows, 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 adrfition of calcium hypochloride is done every 10 mfoutes unfit the 4th hour. After the 4th hour, osddation/leaching tank 42 is emptied. The mixture goes to filter press 32 for dewatering. The pregnant solution PS that contains the leached gold is cotiected 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 I is treated and dean m 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 process uses calcium hypochlorite as the hypochlorite-bearing reagent, sodium chloride to stebize the gold-chioride complex, and caustic soda and hycbochioric a d as pH-rruxfifying reagents. The first stage is a 3 - 4 hours oxidation stage wherein the suffides minerals m the flotation concentrate is axkfized in aticafine conditions. The pH is adjusted to 9.5 at the start and it is monitored throughout the oxidation process. Caustic soda is added to mstiitan 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 hows, wflh weighed amounts of calcium hypochlorite being added aft 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 file gold components of ore and it also allows the dissolution of any gold exposed to the Ex ant In this modified chlorination protocol, die main reagents are sodium hypochlorite, caldum hypochlorite and sodium chloride. In addition, sodium hydroxide and hydrochloric add are used as pH modifiers. Table 1 shows the percent volume of each extraction reagent with respect to the Bxiviant volume.

Table 1 - Percent Volume of Reagents

The developed process that accounts tor the fast production of sulfuric acid without sacrificing die efficiency in dissolving gold through a 2-stage leaching process is performed. The first stage is leaching at alkaline conditions for three horns in order to pariialy oxidize most of the suffides whie preventing any drastic changes in the pH due to the sulfuric add product of the oxidation reaction. This is done by mixing die main reagents for five mireries. Thereafter, 100g of die flotation concentrate is added to the solution. The second stage involves the teaching of the gold exposed from the previous oxidation process and the rest of the free and exposed gold prior to die leaching process. After the first stage, a small amount of hydrochloric add is added to lower die pH. Fixed amounts of caldum hypochlorite are added at time intervals for the whole second stage in order to replenish the amount of Kxhriant 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 1 wil undergo the precipitation process to recover the gold. To precipitate the gold, sodium metabisulfite is added in precipitation container 44. The solution is mixed thoroughly for at least 5 minutes. Thereafter, ascorbic actd is also added. The solution is again mixed thoroughly for at least 5 minutes. The solution is left for about 2 hours to predptate the gold. The solution is then filtered using pressure fHter 45 to separate gold precipitates GP.

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

The tellings from final tails thickener 28 is discharged into final tailings settling pond 51. The sokds are allowed to settle producing dear water CW that can be disposed to a natural body of water like river R. The solids from final tailings seting pond 51 and the barren solids BS from ffiter 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 After 45) are placed m neutrafization tank 52 to neutralize the pH using sodium hydroxide before discharging to the wastewater treatment compartment 53.

The neutrafized barren solution is then discharged from wastewater treatment's 53 first compartment 531. The solution then flows through oooopeaf - zeolite layer 54. The treated water at the bottom of cocopeat-zeofite layer 54 goes to a holding area/empty compartment 55. When this compartment becomes foil, it overflows to second compartment 532 with a cocopeat-zedfte 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 dear water CW, is then discharged to river R.

The preferred embodiment of this invention is described in the above-mentioned detailed description, it is understood that those skied in the art may conceive modifications and/or variations to the embodiment shown and described therein, Any such modifications or variations that fafl within toe purview of this description are intended to be included thereto as wefi. Unless specifically noted, it is the intention of the inventors that the words mid phrases in the specification and claims be given the ordinary and accustomed meanings to those of ordinary ski to toe applicable art The foregoing description of a preferred embodiment and best mode of toe invention known to the appticant at the time of ffiing toe application has been presented and is intended for the purposes of illustration and description. It is not intended to be exhaustive or to Kmit toe present invention to the precise form disclosed, and many modifications mid variations me possible in the Bgtt of the above teachings.

Claims

CLAMS

1. A method for extrading precious minerals comprising toe steps of:

A. crushing an grindmg of ore;

B. concentrating toe crushed ore;

C. dewatering of the concentrate;

D. extracting toe precious metals from the concentrate; and

E treating the taings and wastewater. 2. The method accordmg to dam 1 wherein Step D comprises a chlorination

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

5. The method acoonfing to claim 3 wherein the percent volume of NaOCI wti respect to a lixiviant volume is 50%-80%. 6. The method according to claim 3 wherein the percent volume of Ca(OCI)2 with respect to a lixiviant volume is 6-10%.

7. The method accordmg to claim 3 wherein the percent volume of NaCI with respect to a lixiviant volume is 10-30%.

& The method according to claim 3 wherein toe percent volume of NaOH with respect to a lixiviant volume is 0.5-2%.

9. The method according to claim 3 wherein the percent volume of HCi with respect to a Ibdviart volume is 1-S%.

10. The method accordng to claim 3 wherein the main reagents and the pH mocfifiers have toe following optimal percentage volume to a lixiviant

11. The method according to claim 3 wherein the teachmg process comprises two stages.

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

A. mixing the main reagents for five miiutes; and

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 toe rest of the free and exposed gold prior to the leaching process following the steps of:

A. adring a smal amourt of hydrochloric add to lower the pH;

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

C. filtering the mixture for the precious metal content