AU2010101479A4 - One kind of reclamation and bio-safety disposal method for cyaniding tail slurry - Google Patents

Abstract

Patent Application Number 2010101479 Field of Technology This invention belongs to the comprehensive treatment technology of mine environment protection program involving one kind of reclamation and bio-safety disposal method of cyaniding tail slurry. This method aims mainly to cyaniding tail slurry with cyanide, thiocyanide, heavy metal, arsenic pollutants. This method uses the hydrogen peroxide to process treating the tail slurry under different PH conditions with cyanide, thiocyanate, heavy metal and arsenic pollutants. The conversion rate of sulforhodanide to cyanide is 2::88% and pollutants of cyanide, COD, heavy metal and arsenic reaches to the requirements of sewage water synthesis discharging standard.

Description

One Kind of Reclamation and Bio-Safety Disposal Method for Cyaniding Tail Slurry Field of Technology This invention belongs to the comprehensive treatment technology of mine environment protection program involving one kind of reclamation and bio-safety disposal method of cyaniding tail slurry. This method aims mainly to cyaniding tail slurry with cyanide, thiocyanide, heavy metal, arsenic pollutants. This method uses the hydrogen peroxide to process treating the tail slurry under different PH conditions with cyanide, thiocyanate, heavy metal and arsenic pollutants. The conversion rate of sulforhodanide to cyanide is >88% and pollutants of cyanide, COD, heavy metal and arsenic reaches to the requirements of sewage water synthesis discharging standard. Technical Background The cyaniding tail slurry from gold and other industries contends many kinds of harmful contaminating materials of which cyanide, thiocyanate (one kind of COD), heavy metal and arsenic are the main common kinds of pollutants. At present, the main technical method of treating cyaniding tail slurry domestic and abroad is mainly by nature degradation method, alkali chlorine method, inkoo method , ozonation-process. Methods of nature degradation, alkali chlorine and inkoo are mainly to destroy cyanide without recycle valuable materials from the slurry. The effectiveness of the nature degeneration and inkoo methods to process sulforhodanide is very bad which is not possible for the filtered liquid after processed reach to the state discharge standard of COD. Simultaneously the effectiveness of removing arsenic and heavy metal is also not good. Although the ozonation method can recycle the useful materials with good processing effect to the above pollutants, but its construction and operation cost is high. The utilization rate of ozone is low. It is difficult to industrialized apply of ozone for the high density contents of cyanogens and sulforhodanide tail slurry treatment. Moreover, there are also many processing treatment methods to the filter pressing clean liquid of cyanogen, sulforhodanide, heavy metal and arsenic contented tail slurry domestic and abroad. But the 20-30% moisture content filter residue during the piling process shall produce threats to safety and environment. First, the filter residue shall still releases cyanide, sulforhodanide, arsenic and heavy metal to pollute the underground water when meet with rain water. Second, the filter residue shall release cyanide sulforhodanide, arsenic and heavy metal to cause the cyanide sulforhodanide, arsenic and heavy metal contented out discharging liquid from the tail slurry reservoir exceeding the standard to pollute surface water leaching to potential safety threats to the tail slurry reservoir. This safety threat is more serious in the raining season. Contents of the Invention The purpose of this invention is to provide a kind of reclamation of cyaniding tail slurry and detoxification processing method. This invention overcomes the shortcomings of the past methods of treating the cyanogen, sulforhodanide, heavy metal and arsenic contents tail slurry filter press liquid. This invention full uses hydrogen peroxide to directly treat the cyaniding tail slurry at different PH value to the different reaction mechanism of sulforhodanide and cyanide and the tail slurry itself chemical reaction advantageous of the physic-chemical properties. This invention, first, uses BET surface area of the micro fine ore grain to increase the contact chances of sulforhodanide, cyanide with hydrogen peroxide and the gas liquid two phases contact surfaces through surface adsorption which accelerate the redox reaction speed and the acidification blowing speed; Second, it uses catalytic function of redox reaction in metal material contented gangue (for example, Fe, Cu, etc.) to accelerate the reaction rate of redox reaction without adding catalysts; Third, at the time of hydrogen peroxide solution transforming the sulforhodanide, the high toxic trivalentarsenic can be converted into low toxic and easy treated pentavalent arsenic, Use Fe 3 , Ca 2 in the gangue for neutralization to satisfy the demand of settling arsenic without extra adding of the arsenic settle reagent; Fourth, under the neutral PH value condition, when hydrogen peroxide solution is used to eliminate the remaining cyanide, the metal material (for example Fe, Cu and etc.) in the gangue to precipitate with the difficult redox reaction to remove cyano complex leading to a good effect of eliminating cyanogens. Simultaneously it further removes the remaining sulforhodanide. The cyaniding tail slurry, through this processing method can recover sodium cyanide at the same time to eliminate the toxic function cyanide, COD, As and heavy metal, leading to the filter pressing clear liquid directly discharged or return to process circulation usage without affecting its technical index; The rain water solution from the filter residue will not have secondary pollution. The filter residue can be uses as building material or underground backfilling. Therefore the use of this invention method for cyanogens content tail slurry treatment can bring good environment, economy and social profits. The method of this invention is to directly mix treating the cyaniding tail slurry containing cyanogen, sulforhodanide, heavy metal, arsenic with hydrogen peroxide liquid, the following steps are included: Step I : The Preparation of Reaction Reagent Use liquid with hydrogen peroxide contents as oxidant and strong sulfuric acid as pH value conditioner. The liquid quantity with hydrogen peroxide content and strong sulfuric acid quantity added shall be determined according to the thiocyanic acid root content and PH value in the original mining slurry. Mix the two chemicals with proportion of 1.5:1-3: 1, the hydrogen peroxide and the thiocyanic acid material quantity. The added quantity of the sulfuric acid shall satisfy the regulation of slurry pH value between 1.0-6.0, After the quantity determination of hydrogen peroxide and sulfuric acid in slurry per liter, mix the sulfuric acid in certain density of hydrogen peroxide; The two reagents may not be mixed together while they can be added to the slurry with sulforhodanide at certain time intervals; As this method directly treats the slurry, the consumption of strong sulfuric acid will be increased if there is a large quantity of acid consumer material in the slurry (as carbonate or acid consume metal oxide compound, hydroxide, etc.). Step II : Pre treatment of the Slurry The slurry shall be prep treated before the formal treatment with the required temperature.; Use heating method to pre-treat the slurry for a temperature of 15~60*C. Four heating methods are as the following; 1 electric heating; 2, use biological oxidation tank self reaction to produce heat; 3, heating by fuel oil or gas; 4, use the geo-thermo from the mine for heating. In order to have an even heating, intermittent heating operation shall be adopted to avoid local overheating phenomenon. Mix the slurry at the time of heating. Continual heating shall be conducted in special designed heater. Step III : Slurry Acidization, Oxidize and Blow-off : Put the dosage prepared from step I and the pretreated slurry from step II into the acidified oxidation reactor for reaction with the amount ratio calculated according to step I. At the same time use air liquid proportion of 50-1000:1 to make blow off, with the reaction time 0.5-3h. This step is the core of the invention which explains in the following. 1.This step can be operated continuously or intermittently. The continuous processing can use one or multi stages. When the multi stages process system is used the most critical point is to guarantee the entire flow smoothly. The slurry shall flow steadily in the entire system. This flow requirement can be controlled by the metering pumps between each stage operation. 2.Massive foam may be produced in the operation of this step. They can affect the operation greatly if not conduct defoaming. If foam goes into lye absorption system, the absorption effect of the lye absorption system shall be serious influenced. Therefore antifoaming device must be installed in the reaction container. Anti foaming methods can be carried out by water stress to do antifoaming, mechanical antifoaming and medicament antifoaming. 3 In order to guarantee the safety and the recovery ratio, the reaction must be conducted in a tight sealed system. HCN air blow off can be recycle used or exhausted after lye absorption. 4. In order to maintain the reaction temperature, necessary heat insulation device shall be installed. Electricity heating or heat changer can be used to keep the temperature. 5. In order to prevent HCN blow off air carrying reaction liquid, gas liquid separator shall be installed on the reactor. Step IV : Blow off air can be absorbed by lye liquid The blowing off air with HCN from the acidification oxidation reactor in step III shall be absorbed by lye liquid using 10-30% density hydroxide solution in it. The absorption tower sampling is from packed tower with 915, (25 and 950 packing material of cascade mini ring or multi surface hollow ball padding. The spray density of absorption solution is 2-30m 3 /(m 2 -h). Step V : Neutralization Treatment After processed from step IV the slurry shall be neutralized by lime to 5-9 PH value. Hydrogen peroxide solution shall be applied once again according to the remaining cyanide density in the slurry. The reaction time is 1.5-3h churning with 50-100 air liquid ratio. Clean liquid filter pressed from the treated slurry can be directly discharged or return to processing circulation usage. Send the dried slurry to tail reservoir where within the pH value scope, the remaining cyanide can be fully reacted and removed by hydrogen peroxide solution. Heavy metal cyano complex, heavy metal and arsenic can be stably settled in the gangue and finally be removed from clear liquid by filtering press. The described hydrogen peroxide liquid contain solid calcium superoxide, sodium percarbonate and other chemicals may release peroxide in water solution The beneficial effect of this invention is as the follow : The cyaniding tail slurry treated by this method can remove the toxic functioning cyanide, COD, As and heavy metal at the same time to recover cyanide sodium; The clear liquid after filter pressed can be directly discharged or return to process circulation usage without affecting its technical index; The filter residue liquid solution produced from rain water has no secondary pollution. They can be used as construction material or as underground backfilling material. Therefore, using this invention method to process cyanogen tail slurry shall have good environment, economic and social benefits. This invention using hydrogen peroxide to directly process cyaniding tail slurry has the following advantages compare with previous methods; 1. This method can process many kinds of pollutant by removing heavy metal cyanogen complex with good processing effect.

2.The method can recover cyanide in the slurry. The sulforhodapide conversion rate is high and stable. Through small and extensive experiments, the sulforhodanide conversion rate is >88% . The total recovery ratio can be increased by more than 20% comparing with the same slurry filter clear liquid press processing. 3. The speed of redox reaction and HCN blow off is quick with short time processing. It can treat more volume compare with the same reactor volume load. 4. It can reduce cost to apply less reaction reagent and fully utilize the useful ingredient in tail gangue. 5. The process flow is short, easy for operation and maintenance management. 6. It can prevent secondary pollution from dried tail piles. Detailed Implementation Mode The method of this invention is to mix and treat the cyaniding tail slurry containing cyanogen, sulforhodanide, heavy metal, arsenic with hydrogen peroxide liquid, the following steps are included: Step I : The Preparation of Reaction Reagent Use liquid with hydrogen peroxide content as oxidant and strong sulfuric acid as pH value conditioner. The liquid quantity with hydrogen peroxide content and strong sulfuric acid quantity added shall be determined by the thiocyanic acid root content and pH value in the original slurry. Mix the two chemicals together with a proportion of 1.5:1-3:1, the hydrogen peroxide and the thiocyanic acid material quantity. The added quantity of the sulfuric acid shall satisfy the regulation of slurry pH value between 1.0-6.0, After the quantity determination of hydrogen peroxide and sulfuric acid in slurry per liter, mix the sulfuric acid with certain density of hydrogen peroxide; The two reagents may not be mixed together while they added to the slurry with sulforhodanide at certain time intervals; As this method directly treats the slurry, the consumption of strong sulfuric acid will be increased if there is a large quantity of acid consumer material in the slurry (as carbonate or acid consume metal oxide compound, hydroxide, etc.). Step 1I : Pre treatment of the Slurry Before formal processing, slurry shall be prep treated with the required temperature.; Use heating method for pre-treatment to reach a temperature of 15-60*C. Four heating methods are as the following; 1 electric heating; 2, use biological oxidation tank self reaction to produce heat; 3, heating by fuel oil or gas; 4, use the under ground heating at the mining site for heating. In order to have an even heating, intermittent heating operation shall be adopted to avoid local overheating phenomenon. Mix the slurry at the time of heating. Continual heating shall be conducted in special designed heater. Step III : Slurry Acidization, Oxidize and Blow-off: Put the dosage prepared from step I and the pretreated slurry from step II into the acidified oxidation reactor for reaction with the amount ratio calculated according to step I. At the same time use air liquid proportion of 50-1000:1 to make blow off, with the reaction time 0.5-3h. This step is the core part of the invention which explains in the following; 1. This step can be operated continuously or intermittently. The continuous processing can use one stage or multi stages. When multi stages process system is used the most critical point is to guarantee the entire flow smoothly. The slurry shall flow steadily in the entire system. This flow requirement can be controlled by the metering pumps between each stage operation. 2. Mass ive foam may be produced in the operation of this step. They can affect the operation greatly if not conduct defoaming. If foam goes into lye absorption system, the absorption effect of the lye absorption system shall be serious influenced. Therefore antifoaming device must be installed in the reaction container. Anti foaming methods can be carried out by water stress to do antifoaming, mechanical antifoaming and medicament antifoaming. 3 In order to guarantee the safety and the recovery ratio, the reaction must be conducted in a tight sealed system. HCN air blow off can be recycle used or exhausted after lye absorption. 4. In order to maintain the reaction temperature, necessary heat insulation device shall be installed. Electricity heating or heat changer can be used to keep the temperature. 5. In order to prevent HCN blow off air carrying reaction liquid, gas liquid separator shall be installed on the reactor. Step IV : Blow off air can be absorbed by lye liquid The blowing off air with HCN from the acidification oxidation reactor in step III shall be absorbed by lye liquid using 10-30% density hydroxide solution in it. The absorption tower sampling is from packed tower with 915, 9 2 5 and 950 packing material of cascade mini ring or multi surface hollow ball padding. The spray density of absorption solution is 2-30m /(m 2 -h). Step V : Neutralization Treatment After processed from step IV the slurry shall be neutralized by lime to 5-9 pH value. Hydrogen peroxide solution shall be applied once again according to the remaining cyanide density in the slurry. The reaction time is 1.5-3h churning with 50-100 air liquid ratio. Clean liquid filter pressed from the treated slurry can be directly discharged or return to processing circulation usage. Send the dried slurry to tail reservoir where within the pH value scope, the remaining cyanide can be fully reacted and removed by hydrogen peroxide solution. Heavy metal cyano complex, heavy metal and arsenic can be stably settled in the gangue and finally be removed from clear liquid by filtering press. Real Test Example 1 : Small Batch Process Test Take 2 liter cyaniding tail slurry, add 17ml/L hydrogen peroxide with pH value below 2 condition and the reaction time 2.5h, add equal quantity of strong H 2

SO

4 at constant temperature of 40'C by different gas liquid ratio to carry out conversion blow off. Use absorption column loaded with 3L NaOH solution to absorb HCN After neutralization of lime to pH value 7, add 2.5ml/L hydrogen peroxide to eliminate cyanide. The test effect see Table 1: Table 1 : Cyaniding Tail Slurry Converting into Resources, and Small Size Detoxification Test Result . Oxidized Neutralized Absorption Index items Basic solution solution solution liquid CN ( mg/l ) 7.65 52.41 0.45 SCN mg/l 1820.80 38.70 1.72 COD mg/l) 2300 167.4 90.5 Cu ( mg/l ) 0.78 - 0.21 Recovery rate of Pb ( mg/l ) 0.06 - 0.01 CN is 90.52% Fe mg/l 1.70 - 0.01 As mg/l 0.64 - 0.00 pH value 8.5 2.0 7.0 ( dimensionless ) Real Test Example 2 : Small Size Continuous Test According to the technical condition gained from batch process tests, the continuous test conditions are determined as the follow : (1) Process quantity of slurry : 2L/h (2) Gas liquid ratio : 400:1; ( 3 ) Temperature control : 40'C (4 ) Reagent flow volume : Conversion blow off hydrogen peroxide 30ml/ L

H

2

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4 6ml/ L , CaO6g/ L , de-cyanogen hydrogen peroxide 2.5ml/ L (5 ) Absorption liquid : 15%NaOH 4Lo Test result see Table 2 Table 2 : Cyaniding Tail Slurry Converting into Resources, and Small Detoxification Continuous Test Result . . Oxidized Neutralized Absorption Index i teams Basic solution solution solution liquid CNT- ( mg/l) 6.65 62.41 0.43 SCN ( mg/l ) 1727.55 40.50 1.42 COD ( mg/l ) 2227 145.4 88.5 Cu ( mg/l ) 0.89

-

0.21 Recovery rate of Pb ( mg/l ) 0.06 - 0.01 CN is 88.42% Fe (mg/l ) 1.56 - 0.01 As ( mg/l ) 0.64 - 0.00 pH value pHvaue8.5 2.0 7.0 ( dimensionless ) 8 2 Real Test Example 3 : Medium Size Continuous Processing Test This test uses Step V introduced by this invention. The processing quantity of the tail slurry is 50L/h. adding 20mL/h hydrogen peroxide, 6 mL/h sulfuric acid. Keep the slurry still for 1.5h with the gas liquid ratio at 300:1. The temperature of acidified oxidation is 4000. Conduct the test two times with 8 hours each. The total processed slurry is 840L. See the result in the following Table 3: Table 3 : Cyaniding Tail Slurry Converting into Resources, and Medium Detoxification Continuous Test Result No. of test First time Second time Total Test time ( h )8 8 16 Slurry quantity ( L) 410 430 840 First stage Initial density of CN(%) 0.00 2.12 absorption End density of CN- ( % ) 2.12 4.28 Absorption liquid volume 9 9 CN-recovery quantity( g ) 190.8 194.4 385.2 Second Initial density of CN ( % ) 0.00 0.43 stage End density of CN- ( % ) 0.43 0.94 absorption Absorption liquid volume 9 9 CN-recovery quantity( g ) 38.7 45.9 84.6 The accumulated CN recovery quantity in the absorption solution is 469.8g ; In theory the conversion quantity of SCN~ to CN'shall be 519.7g ; In reality the recovery rate of SCN-is 90.14%. See the test result in Table 4 : Table 4 : Cyaniding Tail Slurry Converting into Resources, and Medium Detoxification Continuous Test Result . Basic Oxidized Neutralized Absorption Index i teams solution solution solution liquid CNT- ( mg/l) 6.65 62.41 0.42 SCN ( mg/l) 1727.55 40.50 1.50 COD ( mg/l ) 2227 145.4 78.5 Cu ( mg/l ) 0.89 - 0.20 Pb ( mg/l ) 0.06 - 0.01 Recovery rate of CN is Fe ( mg/i ) 1.56 - 0.01 90.14% As ( mg/l) 0.64 - 0.00 pH value pHvaue8.5 2.0 7.0 ( dimensionless ) According to the intermediate test to a mining industrial company using the method of this invention to recover cyanide from cyaniding slurry and recover cyanide from cyaniding slurry filter liquid for comparison. And the total quantity of the recovered cyanide, year total operation cost, expenses and the investment expenses are analyzed. It proves that the direct processing of cyaniding tail slurry using this invention method has more advantages over the filter pressed treatment of the same slurry It is the best scheme reasonable in economy, feasible in technology and acceptable to environment. The designed daily treatment capability of a certain mining industrial company is to process gold ore concentrate 750t/d which produces approximately 2160m 3 /d cyanoding tail slurry. The project scale of processing cyaniding slurry capability is 2160m 3 /d with production date of 330d/a. The barren fluid contends sulforhodanide 2612.80mg/L. The product plan is for liquid cyanide sodium. See the comparisons in Table 5 and Table 6. Table 5 : T reatment of Cyaniding Tail Slurry No. Particulars Treatment of cyaniding tail slurry 1.The total cyanide recovery rate from the sulforcyanide is 88% , the rate of resources utilization is more than 60% ; Total quantity of sodium 2.Resource utilization rate of water recycling cyanide recovery is 83.48% , the rate of industrial waste water recycle utilization rate is more than 70% 3.No secondary cyanide pollution to surface water. Recycling water profit 103.42 (ten thousand yuan) Cyanide recovery rate (%) 88 Total sodium cyanide 1203.19 recovery (ton/a) Total yearly income of sodium cyanide (ten 1964.81 thousand yuan!/year) 1. Operation cost of advanced treatment is low Operational cost 2. Maintenance cost of tail slurry reservoir is low 2 Unit cost (yuan/ m3) 22.65 Yearly quantity of treatment 71.28 (ten thousand m3/a) Yearly operational cost 1614.49 ___ (ten thousand yuan/a) 3 Investment expenses 3190 (ten thousand yuan) 4 Annual profit 453.74(gain) ( ten thousand yuan) n 5 Environment benefit Get preferential policy of energy saving and emission reduction from the nation 6 Social benefit Strong competitive ability in national resources development Table 6 : Filter Press Treatment of Cyaniding Tail Slurry No. Treatment of . filter press liquid - Particulars (including sulfocyanide waste water) 1. Total cyanide recovery rate from sulforcyanide is 45.5% , the rate of resources utilization is less than Total quantity of sodium 60% 60% ; cyanide recovery 2. Utilization rate of water recycling is 83.48% , the rate of industrial waste water recycle utilization rate is Recycling water profit 103.42 (ten thousand yuan) Cyanide recovery rate 45.58 Total sodium cyanide 626.41 recovery (ton/a) Total yearly income of sodium cyanide (ten 1022.93 thousand yuan/ year)/a) 1.Operational cost of advanced treatment is high Operational cost 2. Maintenance cost of tail slurry reservoir is high 2 Unit cost (yuan/ m3) 29.16 Yearly quantity of treatment (ten thousand 51.71 m3/a) Yearly operational cost 1507.86 (ten thousand yuan/a) 3 Investment expenses (ten thousand yuan) 4 Annual profit -381.51(loss) (ten thousand yuan) Efficient filter presser, advanced 5 Supporting facilities treatment system in the tail slurry added reservoir, slurry reservoir anti leakage, cyanide dreg treatment system, etc. To summarize from the above, the state of process art of direct regeneration of cyanide from tail slurry pollutant containing cyanide, thiocyanate, heavy metal and arsenic is short and the sulforhodanide conversion rate is stabilized at >88%. This method can convert and recover sulforhodanide from the 30% moisture content in the filter pressed tail slurry compared with the cyanide recovery from the tail slurry filter pressed liquid with sulforhodanide. So it has a much better economic profit; Moreover this method of invention has advantages of avoiding secondary pollution from the dried tail slurry piles. That's why the regeneration capability of cyanide from polluted tail slurry with cyanide, thiocyanate, heavy metal, arsenic contents and so on etc has much more value.

This invention publicized one kind of method to convert cyaniding tail slurry into resources and detoxification treatment processing. This method is to directly co-treat the cyaniding tail slurry containing sulforhodanide, heavy metal and arsenic with the liquid containing hydrogen peroxide. This invention uses the BET surface area of the micro fine grain minerals, through surface absorption function to increase the contact chances of sulforhodanide with hydrogen peroxide and the gas liquid phases contact dimensions, accelerate the redox reaction speed and acidification blow off speed. By utilizing the metal matter in the mining slag can accelerate the reaction rate of the redox reaction without adding catalyst. The cost can be reduced. When conducting neutralization; use Fe 3 + in the mineral slag to satisfy the arsenic settlement needs without adding extra arsenic settling reagent; When hydrogen peroxide liquid eliminating remaining cyanide, it can also form precipitation with cyano complex which is difficultly to be removed through redox reaction. It can further remove the remaining sulforhodanide. The conversion rate of the sulforhodanide in the slurry is ;>88%, and increase the recovery rate by more than 20% in contrast with the same slurry filter press clear liquid processing treatment.

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Claims (1)

1. 50-1000:1 to make blow off, with the reaction time 0.5-3h. This step is the core of the invention which explains in the following. 1. This step can be operated continuously or intermittently. The 20 continuous processing can use one or multi stages. When the multi stages process system is used the most critical point is to guarantee the entire flow smoothly. The slurry shall flow steadily in the entire system. This flow requirement can be controlled by the metering pumps between each stage operation. 25 2. Massive foam may be produced in the operation of this step. They can affect the operation greatly if not conduct defoaming. If foam goes into lye C :NRPob\DCC\E 727335_1 DOC-6/29/2011 - 18 absorption system, the absorption effect of the lye absorption system shall be serious influenced. Therefore antifoaming device must be installed in the reaction container. Anti foaming methods can be carried out by water stress to do antifoaming, mechanical antifoaming and medicament 5 antifoaming. 3 In order to guarantee the safety and the recovery ratio, the reaction must be conducted in a tight sealed system. HCN air blow off can be recycle used or exhausted after lye absorption. 10 4. In order to maintain the reaction temperature, necessary heat insulation device shall be installed. Electricity heating or heat changer can be used to keep the temperature. 5. In order to prevent HCN blow off air carrying reaction liquid, gas liquid 15 separator shall be installed on the reactor. Step IV : Blow off air can be absorbed by lye liquid The blowing off air with HCN from the acidification oxidation reactor in 20 step III shall be absorbed by lye liquid using 10-30% density hydroxide solution in it. The absorption tower sampling is from packed tower with 915, <p 2 5 and p 5 0 packing material of cascade mini ring or multi surface hollow ball padding. The spray density of absorption solution is 2-3Om 3 /(m 2 -h). 25 Step V : Neutralization Treatment C :RPonblDCC\EJL\3727335_ .DOC.6/29/2011 - 19 After processed from step IV the slurry shall be neutralized by lime to 5-9 PH value. Hydrogen peroxide solution shall be applied once again according to the remaining cyanide density in the slurry. The reaction time is 1.5-3h churning with 50-100 air liquid ratio. Clean liquid filter pressed 5 from the treated slurry can be directly discharged or return to processing circulation usage. Send the dried slurry to tail reservoir where within the pH value scope, the remaining cyanide can be fully reacted and removed by hydrogen peroxide solution. Heavy metal cyano complex, heavy metal and arsenic can be stably settled in the gangue and finally be removed from 10 clear liquid by filtering press. The described hydrogen peroxide liquid contain solid calcium superoxide, sodium percarbonate and other chemicals may release peroxide in water solution.