DOE CYANIDE. Recolection

7/23/2019 DOE CYANIDE. Recolection

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CENTRO DE ENSEÑANZA TÉCNICA Y SUPERIOR

Engineering School

DOE

"Cyanide recovering & regeneration

From industrial effluents (gold & silver metals extraction process)”

Samantha Páez 14633

Tijuana B.C. October 1, 2015.



CYANIDE RECOVERY TECHNOLOGY COMPARISON1

Legislation in most gold mining regions of the world demands that gold plants meet rigorous

environmental standards with respect to cyanide. These requirements can be met either by destroying

cyanide after a single pass through the gold plant or by recovering cyanide from the tailings and recycling it

to leaching. Although cyanide recovery processes are not yet widely practiced, the technologies are fairlysimple, both from chemistry and process engineering perspectives, and they have the potential to yield

significant economic and environmental benefits.

AVAILABLE TECHNOLOGIES FOR CYANIDE RECOVERY

There are several processes for recovering cyanide from gold plant tailings that are available to the

mining industry.

1. Cyanisorb (AVR: Acidify, volatilize and reneutralize)

2. SART (Sulphidize, acidify, recycle and thicken)

3. Hannah (Strong base resin extraction of free cyanide and metal cyanide species)

4.

AuGMENT (Strong base resin extraction of copper and cyanide). SGS metallurgical group has beeninvolved in the development of all of these processes and can determine the advantages and

disadvantages of each.

COST EFFECTIVENESS IS CRITICAL

The cost of cyanide consumption and destruction can be a significant percentage of total operating

costs on a gold plant, and unlike other operating costs, yields no economic “return”. The choice of the best

strategy for handling cyanide in the tailings can therefore have a major influence on the economic health of

a project. The economic impact of cyanide is different in every operation, but it is possible to compare cyanide

destruction and cyanide recovery costs for a fairly generic high cyanide consuming case. The capital cost of

a cyanide recovery plant could pay back in less than 2 years in many cases, particularly when high cyanide

consumption is associated with copper mineralization in the ore. As a broad generalization, cyanide recovery

will produce more favorable economics than cyanide destruction in those cases where potentially recoverable

cyanide consumption is greater than 1 kg/t NaCN, or exceeds 1000 tons NaCN per annum.

WHY RECYCLE CYANIDE? LOWER COSTS

• Recycled cyanide is 2-3 times cheaper than new cyanide.

• Reduced detoxification costs.

• Opportunity to sell by-products such as copper sulphide.

LESS ENVIRONMENTAL RISK

• Reduced loading of potentially harmful salts in the tailings and recycle water (e.g. CNS, CNO, NH 3 andmetal cyanides).

• Less new cyanide is needed, so there is less transported, stored and handled, reducing the risk of spills.

1CYANIDE RECOVERY: http://www.sgs.mx/~/media/Global/Documents/Flyers%20and%20Leaflets/SGS-MIN-

WA016-Cyanide-Recovery-Comparison-EN-11.pdf



So as we learned Cyanide ion (CN-) is used for precious (Gold & Silver) metals extraction process

because CN- make very stable compounds in solution. The disadvantage is CN- has a very high toxic levels,

so it is important recover the CN- & avoid impact the environment within effluents.

Recover it or "reuse" (regeneration) are options to avoid effluents with high levels of CN-.

Next data come from experimental work using pressured air through porous tube. Air - porous tubegenerate very fine bubbles which extract the CN- as gas from the solution (effluent) & release the effluent

from the CN-.

After that the CN- recovered into the experiment, can be used again to extract metals.

The data table contains:

1. CN- solution flow (liter / minute)

2. Rate (proportion) air versus solution.

NOTE: Is expected higher air proportion means higher recovering rate means Lower CN- concentration into

effluent.

Cyanide (CN-) remaining within effluent (CN- not recovered) (5 repetitions)

The objective for the experiment is demonstrates if there is some relation between PROPORTION Air-

Solution (FACTOR) & CN- not recovered (RESPONSE)



Initial Concentration forCN-

250 mg / liters

Air flow 210 Liters/min

CN- Not recovered present within effluent (mg/liters)

CN- solution flow(liters/min) PROPORTION Air / Solution Rep 1 Rep 2 Rep 3 Rep 4 Rep 5

50 4.20 172 202 176 190 181

40 5.25 120 109 104 125 116

30 7.00 94 86 105 100 96

20 10.50 39 66 49 48 50

Table 1. Data received from the experiment

1. Give both hypothesis (name & formula).

2. Calculate % of recovery for each treatment. % Recovering = (Initial Concentration - Conc. Not

recovered)/Initial Conc.

3.

Obtain chart % of recovering versus Proportion air-solution.a. Indicate what kind of relation is there? (Direct / Reverse; linear, nonlinear, etc.

b. What happen with % of recovering if we use more air? Increase or decrease?

4. Apply all methods recommended by MINITAB using ANOVA to detect if there is statistical difference

a. FACTOR: PROPORTION AIR – SOLUTION

b. RESPONSE: Concentration not recovered

5. Built on CHARTS with AVERAGE & BLOCKS to confirm if there is difference (No overlap)

6. Conclusions. Differences between each pair compared

7. Obtain 4 in 1 charts for RESIDUALS

8. Analyze R2 for linear model



EXPERIMENT

Hypothesis: Given the last information is expected to higher air proportion, higher recovering rate and lower

CN- concentration into effluent. In simple words, to more pressure given, more cyanide recover.

RESULTS

Air/Solution Proportion(liter/minute)

Not Recovery Cyanide(mg/liter)

FITS RESI FITS_1 RESI_1

4.20 172 184.20 -12.20

184.20 -12.20

4.20 202 184.20 17.80 184.20 17.80

4.20 176 184.20 -8.20 184.20 -8.20

4.20 190 184.20 5.80 184.20 5.80

4.20 181 184.20 -3.20 184.20 -3.20

5.25 120 114.80 5.20 114.80 5.20

5.25 109 114.80 -5.80 114.80 -5.80

5.25 104 114.80 -10.80

114.80 -10.80

5.25 125 114.80 10.20 114.80 10.20

5.25 116 114.80 1.20 114.80 1.20

7.00 94 96.20 -2.20 96.20 -2.20

7.00 86 96.20 -10.20

96.20 -10.20

7.00 105 96.20 8.80 96.20 8.807.00 100 96.20 3.80 96.20 3.80

7.00 96 96.20 -0.20 96.20 -0.20

10.50 39 50.40 -11.40

50.40 -11.40

10.50 66 50.40 15.60 50.40 15.60

10.50 49 50.40 -1.40 50.40 -1.40

10.50 48 50.40 -2.40 50.40 -2.40

10.50 50 50.40 -0.40 50.40 -0.40

Table 2. Results of the experiment



Graphic 1. Not Recovery Cyanide

As we see in table 1, the less air pressure we give, the less recover cyanide we get. That means so far, our hypothesis is correct. Now we have to

prove it as we make the following analysis.

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210

4.20

5.25

7.00

10.50

Not recovery Cyanide (mg/Liter)

A i r P r e s s u r e ( L i t e r / m i n )

NOT Recovery Cyanide (mg/liter)



Initial Concentration

for CN-

Air/SolutionProportion

Not RecoveryCyanide

250

(Liter/minute) (mg/liters)Not recoveredCyanide (%)

RecoveredCyanide (%)

4.20

172 69% 31%

202 81% 19%

176 70% 30%

190 76% 24%

181 72% 28%

5.25

120 48% 52%

109 44% 56%

104 42% 58%

125 50% 50%

116 46% 54%

7.00

94 38% 62%

86 34% 66%

105 42% 58%

100 40% 60%

96 38% 62%

10.50

39 16% 84%

66 26% 74%

49 20% 80%

48 19% 81%

50 20% 80%

Table 3. Cyanide Percentage Recovered



Graphic 2. Recovered Cyanide (%)

As we saw in the graphic above there is a direct linear relationship, because if we increase the air pressure

we obtain more cyanide from the solution, so the recovered percentage of the cyanide increase as well, just

as we expected.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

4.20 5.25 7.00 10.50

P e r c e n t a g e o f R e c o v e d C y a n i d e ( % )

Air Pressure (Liter/minute)

Recovered Cyanide (%)



ANOVA

As we can see in the graphic the interactions between this four different pressures are almost none. However at first

sight we can appreciate some interaction between the results of 5.25 pressure and 7 pressure Liter/minute

However if we go through the numbers in a more specific way, we’ll see that the last number of 5.25 Liter/minute is

104 and the first number of 7 Liter/minute is 105, so there is really no interaction. The blue dots means where the mean

is placed and the grey ones are the variations. (All the results of the experiment).



In this graphic the little dots are the average of data, the horizontal line is the median and we can appreciate the

minimum and maximum value of every experiment, which give us the confidence intervals.

If there is no overlap in the data so that means every experiment is different form one another and there is no interaction

or interference with each other. (Significate difference)

As I said earlier, even though it seems there is an overlap, there is none.



If we see the histogram we know there is a tendency for a normal equation, and as we wanted almost all the data

concentrates in zero. However at the edges of the line tendency the model loses its strength. Our main goal would be

all the data concentrated in zero.



In this graphic we can see that the confidence intervals goes through 184.2 at 4.20 Liter/minute to 50.4 at 10.5

Liter/minute.



Again the difference between 5.25 Liter/minute and 7 Liter/minute pressure is almost imperceptive and that is why this

is the data closer that zero.



For the Dunnett I tested both 10.5 Liter/minute and 7 Liter/minute because I wanted to know if it would be some

significant difference and I also wanted to know if this particularly change could give more points with my boss in case

this would be an actual problem in the Company.

While the data is closer to zero, the less effect had the experiment with one another.



In this case, contrary of what we had been doing, if the data touches zero, that means there is a significant different in

the experiments.



In this six comparisons we can appreciate all the interactions the different air pressures have with one another. However

we can see that the 7.00 – 5.25 factor is closer to zero. That means that the relevance of the interaction in almost

inexistent. To the contrary of the pressure 10.50 – 4.20, where the relevance of different pressures is more relevance

to the Cyanide recovery.



One-wayANOVA: Not Recovery Cyanide versus Air/Solution Proportion

Method

Null hypothesis. All means are equal

Alternative hypothesis At least one mean is differentSignificance level α = 0.05

Equal variances were assumed for the analysis.

Factor Information

Factor Levels Values Air/Solution Proportion 4 4.20, 5.25, 7.00, 10.50

Here we see four different levels that equals 4.20 Liter/minute, 5.25 Liter/minute, 7 Liter/minute and 10 Liter/minute.

Analysis of Variance

Source DF Adj SS Adj MS F-Value P-Value Air/Solution Proportion 3 46317 15439.1 171.35 0.000Error 16 1442 90.1Total 19 47759

As we see our F-Value is high which is good and our P-Value is zero which is perfection.

Model Summary

S R-sq R-sq (adj) R-sq(pred)9.49210 96.98% 96.42% 95.28%

Here we can see that the r-squared is actually awesome, because it’s more that 85% that is the minimum request. And we have it almost 10% higher.

Means

Air/SolutionProportion N Mean StDev 95% CI4.20 5 184.20 12.01 (175.20, 193.20)5.25 5 114.80 8.41 (105.80, 123.80)7.00 5 96.20 7.09 (087.20, 105.20)10.50 5 50.40 9.76 (041.40, 059.40)Pooled StDev = 9.49210



Tukey Pairwise Comparisons

Grouping Information Using the Tukey Method and 95% Confidence

Air/SolutionProportion N Mean Grouping

4.20 5 184.20 A5.25 5 114.80 B7.00 5 96.20 C

10.50 5 50.40 D

Means that do not share a letter are significantly different.

Tukey Simultaneous Tests for Differences of Means

Difference, Difference SE of AdjustedOf Levels of Means Difference 95% CI T-Value P-Value

5.25 - 4.20 -69.40 6.00 (-086.59, -52.21) -11.56 0.0007.00 - 4.20 -88.00 6.00 (-105.19, -70.81) -14.66 0.00010.50 - 4.20 -133.80 6.00 (-150.99, -116.61) -22.29 0.0007.00 - 5.25 -18.60 6.00 (-035.79, -01.41) -3.10 0.03210.50 - 5.25 -64.40 6.00 (-081.59, -47.21) -10.73 0.00010.50 - 7.00 -45.80 6.00 (-062.99, -28.61) -7.63 0.000

Individual confidence level = 98.87%

Again, our P-Value is almost zero every time.

Tukey Simultaneous 95% CIs

Fisher Pairwise Comparisons

Grouping Information Using the Fisher LSD Method and 95% Confidence

Air/SolutionProportion N Mean Grouping4.20 5 184.20 A5.25 5 114.80 B

7.00 5 96.20 C10.50 5 50.40 D

Means that do not share a letter are significantly different.



Fisher Individual Tests for Differences of Means

Difference, Difference SE of AdjustedOf Levels of Means Difference 95% CI T-Value P-Value5.25 - 4.20 -69.40 6.00 (-082.13, -56.67) -11.56 0.0007.00 - 4.20 -88.00 6.00 (-100.73, -75.27) -14.66 0.000

10.50 - 4.20 -133.80 6.00 (-146.53, -121.07) -22.29 0.0007.00 - 5.25 -18.60 6.00 (-031.33, -5.87) -3.10 0.007

10.50 - 5.25 -64.40 6.00 (-077.13, -51.67) -10.73 0.00010.50 - 7.00 -45.80 6.00 (-58.53, -33.07) -7.63 0.000

Simultaneous confidence level = 81.11%

Fisher Individual 95% CIs

Dunnett Multiple Comparisons with a Control

Grouping Information Using the Dunnett Method and 95% Confidence

Air/SolutionProportion N Mean Grouping10.50 (control) 5 50.40 A4.20 5 184.205.25 5 114.80

7.00 5 96.20

Means not labeled with the letter A are significantly different from the control level mean.

Dunnett Simultaneous Tests for Level Mean - Control Mean

Difference, Difference SE of AdjustedOf Levels of Means Difference 95% CI T-Value P-Value4.20 - 10.50 133.80 6.00 (118.24, 149.36) 22.29 0.0005.25 - 10.50 64.40 6.00 (48.84, 79.96) 10.73 0.0007.00 - 10.50 45.80 6.00 (30.24, 61.36) 7.63 0.000




Dunnett Simultaneous 95% CIs

Hsu Multiple Comparisons with the Best (MCB)

Hsu Simultaneous Tests for Level Mean - Smallest of Other Level Means

Difference, Difference SE of AdjustedOf Levels of Means Difference 95% CI T-Value P-Value4.20 - 10.50 133.80 6.00 (00.00, 147.17) 22.29 0.0005.25 - 10.50 64.40 6.00 (0.00, 77.77) 10.73 0.0007.00 - 10.50 45.80 6.00 (0.00, 59.17) 7.63 0.00010.50 - 7.00 -45.80 6.00 (-59.17, 0.00) -7.63 0.000


Dunnett Multiple Comparisons with a Control

Grouping Information Using the Dunnett Method and 95% Confidence

Air/SolutionProportion N Mean Grouping7.00 (control) 5 96.20 A4.20 5 184.205.25 5 114.80

10.50 5 50.40

Means not labeled with the letter A are significantly different from the control level mean.

Dunnett Simultaneous Tests for Level Mean - Control Mean

Difference, Difference SE of AdjustedOf Levels of Means Difference 95% CI T-Value P-Value4.20 - 7.00 88.00 6.00 (72.44, 103.56) 14.66 0.0005.25 - 7.00 18.60 6.00 (03.04, 34.16) 3.10 0.018

10.50 - 7.00 -45.80 6.00 (-61.36, -30.24) -7.63 0.000




Conclusion:

In conclusion we can agree that our hypothesis is correct and as we said, if we increase the air pressure solution we

can recover more cyanide than if we use less air pressure solution.

In this experiment using 10.5 liters/min. give us the best combination to accomplish our goal.

Referencies:

Congreso Internacional de Metalurgia (Caracas)

Metalurgia 1997 (Acapulco)Tesis de Posgrado ITS 1997: Concurso Nacional de Creatividad Posgrado 1997

CYANIDE RECOVERY:

http://www.sgs.mx/~/media/Global/Documents/Flyers%20and%20Leaflets/SGS-MIN-WA016-Cyanide-Recovery-

Comparison-EN-11.pdf