CA2224016A1 - Method for producing caro's acid - Google Patents
Method for producing caro's acid Download PDFInfo
- Publication number
- CA2224016A1 CA2224016A1 CA 2224016 CA2224016A CA2224016A1 CA 2224016 A1 CA2224016 A1 CA 2224016A1 CA 2224016 CA2224016 CA 2224016 CA 2224016 A CA2224016 A CA 2224016A CA 2224016 A1 CA2224016 A1 CA 2224016A1
- Authority
- CA
- Canada
- Prior art keywords
- acid
- caro
- water
- mixture
- slurry
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B15/00—Peroxides; Peroxyhydrates; Peroxyacids or salts thereof; Superoxides; Ozonides
- C01B15/055—Peroxyhydrates; Peroxyacids or salts thereof
- C01B15/06—Peroxyhydrates; Peroxyacids or salts thereof containing sulfur
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Physical Or Chemical Processes And Apparatus (AREA)
Abstract
A process for reducing or eliminating Caro's acid mist, created when producing a hot mixture containing Caro's acid by reaction of sulfuric acid and hydrogen peroxide, is carried out by quenching the hot Caro's acid mixture with water to both cool and dilute the Caro's acid.
Description
W O 97/00225 PCTrUS96/10475 METHOD FOR PRODUCING CARO S ACID
The invention is in the field of producing Caro's acid by reaction of s hydr~gen peroxide and sulfuric acid in a controlled and effective manner.
Caro s acid which is peroxymonosulfuric acid is a strong oxidi~i, ,9 cor"pound which has been suy~ested for use in any applicdlions including pulificalion of cyanide-containing effluents by conversion of their cyanides into non-toxic derivatives. Caro's acid is usually produced by reacting togetl,er cGr,cenl,dted sulfuric acid (85% to 98% by weight H2SO~) with cGncentrated hydrogen peroxide (50% to 90% by weight H2O2) to produce an equilibrium mixture of Caro's acid containing peroxy",onosulfuric acid (H2SOs), sulfuric acid and hyd,ogen peroxide. I lov:ever, since the Caro s acid is not stable for long periGJs it must be made and imme~ tely used on site or quickly cooled and stored at refrigerated te",per~lures. In general, theCaro's acid is manufactured on site as needed and in just the amounts required for the specified ap~l c~tion without the necessity of having to store any excess amounts.
One procedure for producing Caro s acid is set forth in U.S. Patent No.
3 900 555 by using an apparatus descril,ed in U.S. Patent No. 3,939 072 for mixing the sulfuric acid and hydlogen peroxide and cooling the mixture with a water-cooled jacket to prevent overhearing of the reactants and premature clecGI~position of the monoperoxysulfuric acid product. These ~,atents teach the use of the monoperoxysulfuric acid product for treating waste aqueous effluents from an electroplating plant containing cyanide ions while simultaneously adding an alkali in amounts suitable for neutralizing the added acid. This assures that the pH of the treated solution in maintained at a specified alkaline value, nommally pH 9, by neutralizing any acidity resultingfrom the added acid.
Another procedure is set forth in U.S. Patent No. 4 915 849 wherein the Caro s acid is used to treat cyanide-containing effluents from an ore-p.ocessing plant. The Caro s acid is manufactured by reacting sulfuric acid with hydrosJen peroxide in propo,liGns cor,espol-ding to between 0.01 and 0.5 moles of sulfuric acid per mole of hydrogel) peroxide. The resulting acid is then added to the cyanide-containing effluent simultaneous with aqueous lime or sodium hydroxide mixtures in order to maintain the effluent at the preferred pH of between 9.5 and 11.5.
Still another procedure is set forth in PCT Publication No. WO
92/07791, a published patent ~pplic~tion of Lane et al., which teaches s production of peroxy.,.Gnosulfuric acid by introducing a hyd~ùgen peroxide solution into a stream of sulfuric acid ~lu~:;, ~y through a reaction chamber, the HzO2 intro~luction being made between the sulfuric acid inlet and the reaction mixture outlet. Both the hyd~ùgen peroxide solution and sulfuric acid are introduced under pressure into the closed tubular reaction cl ,aml,er of the invention. In the reaction, chamber, the through-put per minute of the reaction chamber is at least about 20 times its intemal volume measured b~l~con the inlet for the hyd~oge" peroxide and the outlet.
In carrying out the production of Caro's acid in industrial ~pl)lic~lions, two prùble."s have arisen in the scale-up of the Caro's acid generating unit to commercial proportions. The first prùble." is the protection of a large amount of hyd~os;en peroxide in storage tanks, used to feed the Caro's acid producing generator, from possible conta"-i.,ation. The need to prevent contamination of this large hydloyel1 peroxide source from either Caro's acid, sulfuric acid, or other such impurities is critical to the safe containment and use of the hy.l.ogen peroxide. The second problem is to control the Caro's acid reaction so that the Caro's acid is folllled efficiently with maximum use of the hydloyen peroxide reagent and without having the hot reaction mixtur formed during the reaction go out of control and overflow or rupture the reaction chamber.
2s With respect to the first problem, it has been the custom in the industry to isolate the storage tank of peroxide from the reactor where Caro's acid is pro~!lce-l by means of an intermediate tank (sG"-eli",es called a "break"
tank) to interrupt the stored hydroyel, peroxide source from the line deliveringhydrogen peroxide to the Caro's acid generator. The peroxide from the storage tank is passed by pump means or by gravity into the top of an intemnediate tank to a given level in the intermediate tank without requiring a direct liquid connection b~t~Joon the perùxide in the intermediate tank and the line flowing from the storage tank. This assures that any possible contamination which may be sucked back from the Caro's acid generator into the i"te""eJiate tank will not be able to flow into the hy.J,uyel) peroxide storage tank.
The secG"d problem arises bec~l~se the reaction of sulfuric acid and hyJu~gen peroxide is an exothemmic reaction and some h~,d~oyell peroxide JecGI"poses to fomm large amounts of gas which may cause pressure build up capable of rupturing the reactor or causing the reagents to overflow. This may cause the hot reaction mixture to go out of control with the waste of both sulfuric acid and hydrogen peroxide and further, if no break tank is used, may become a possiblE source of conta",i"alion of the hyJ,ugen peroxide storage 10 tank if it backs up into the hyclrogen peroxide line conl-e~;ti,-3 the hydroyell peroxide storage tank to the Caro's acid reactor.
In copending U.S. Application Serial No. 08/351 987 filed Decer,lber 8 1994, (now Patent No. 5 470,564) in the names of James L. Manganaro et al. a process is described that overcomes the fore~oi. ~y problems. This process for producing Caro's acid is carried out by reacting sulfuric acid having an cGncel llraliGn of at least about 85% by weight and hydrogen peroxide having a cGncenl~dlion of at least about 50% by weight wherein the hydrogen peroxide is introduced through a first feed line and the sulfuric acid is introduced through a second feed line into a funneling zone open to the atmosphere, the first feed line and secGn d feed line having air gaps between their ends and the funneling zone, passing said hyd-ogen peroxide and sulfuric acid by gravity flow from said funneling zone into one end of a reaction zone that has been sized to permit a pressure drop therein which is at least 8 times the theoretical pressure drop for liquids flowing through such reaction zone and removing a mixture containing Caro's acid from an exit end of the reaction zone.
While the above process has been very suGcessful in eliminating the need for break tanks and avoiding pressure buildups in the reactor, the Caro s acid that issues from the end of the reactor open to the atmosphere is quite hot bec~use of the exothemmic reaction between the sulfuric acid and h~,J,ogen peroxide and tends to form an undesiled Caro s acid mist. The Caro's acid mist is an irritant to the mucus ",eull,ranes of workers who are in the vicinity of the outlet of the Caro s acid reactor. The mist is especially objectionable when the reactor is inside a building where the mist can collect and build up in conce"lf~lion to a point where protective gear and/or special W O 97/00225 PCTrUS96/10475 exhaust provisions are required. Even outdoors the mist is notice~hlQ and most objectionable to any workmen who may be downwind from the Caro's acid reactor. Further, when the Caro's acid is used to treat tailing slurries toreduce their cyanide conce"l,dlions, the mixing of the Caro's acid with the tailing slurries is not instanlaneous due to the syrupy nature of the COI Ice, Itrdl6cl Caro's acid that issues from the Caro's acid generator and thehigh density of the tailing slurries (35% to 40% solids). This is undesired bec~l ~se it allows time for the Caro's acid to decompose before reacting with the cyanide in the tailing slurry.
It has now been found that the Caro's acid mist, that fomms when Caro's acid is produced by reaction of sulfuric acid and hyd~ogen peroxide in a reaction zone and the hot Caro's acid mixture is released from the end of the reaction zone, can be reduced or eliminated by quenchi. ,9 the hot Caro's acid mixture with water to both cool and dilute the Caro's acid.
In carrying out the present invention, the Caro's acid is produced by reacting sulfuric acid and hydrogen peroxide together, preferably in a continuous manner and in accordance with the process set forth in our copending U.S. Ar, '.c~tion SN 08/351,987filed Dece"lber8, 1994 (now Patent No. 5,470,564) in the names of James L. Manganaro et. al. While other processes may also be employed for producing the Caro's acid, this is the preferred method bec~l~se the Caro's acid is for",eJ efficial,lly with maximum use of hyclrogel) peroxide reagent and without having the hot reaction mixture fommed during the reaction go out of control and overflow or rupture the reaction chamber. In this process the reactants are added into a funneling zone, or other type of feeding zone, open to the alrnosphere and then the hydrogen peroxide and sulfuric acid flow from the funneling zone by gravity into one end of a reaction zone where the reaction takes place. The reaction zone which is loc~ted downstream from the funneling zone is preferably a pipe-like or tube reactor, whose diameter may be variable or constant, which may be either vertically oriented or h~ri~o,ltally oriented or any skew angle intermediate these two extremes and is fed by gravity from the funneling zone. Further, it is preferred that the reaction zone have a size which pemmits a pressure drop in the reaction zone which is at least eight times the theoretical pressure drop for liquids passing through such reaction zone. Such reaction zones are nommally static reactors containing several mixing elements which ensure a complete mixing and reaction of the two reagents.
The sulfuric acid employed in the reaction can be of any c~r,ce, ll-dliO"
from about 85% by weight to about 98% by weight H2SO4 with about 93% by s weight sulfuric acid being preferred bec~use of its ready availability and workability. The hydr~gen peroxide employed can be of any conce"l,dlio from about 50% by weight H202 to about 90% by weight H202 with 70% by weight hyd~oyel, peroxide being ~,refer,tzd bec~use of safety considerations and availability. The mole ratios of sulfuric acid to hydr~yel, peroxide lo (H2SO4/H202) can range from about 1/1 to about 4/1 with about 2/1 to about 3/1 being prefe~.ed. The reaction results in Caro's acid being formed in a solution which is an equilibrium mixture of hydrogen peroxide, sulfuric acid, Caro's acid and water. The equation for this reaction is set forth below:
H2S~4 + H2~2 ~ H2SOs + H20 A typical cGl"~,osilion prepared from a 2.5/1 mole ratio of 93 weight percel ,l sulfuric acid and 70 weight percent hydrogel) peroxide is as follows:
Caro's Acid (peroxymonosulfuric acid) 25 weight percent; sulfuric acid 57 weight percent; hydrogel) peroxide 3.5 weight percent; and water 14.5 weight percel,t. A cG"si~lerable amount of heat is rcloascd as a result of mixing the hydrogen peroxide with sulfuric acid. The amount of heat rel ~ced depends on the concenlrdliGI) of the starting reagents and the mole ratios of sulfuric acid to hydrogen peroxide. Using the preferred cGncenlrdliol)s of 70 weight percent H202 and 93 weight percent H2SO4 and a preferred mole ratio of H2SO4/H202 of 2.5/1, an increase in te.n~.eralure of 58QC will occur. If, for example, the raw materials are at 34~C, the Caro's acid will reach a temperature of 92~C.
Caro's acid mist is generated as the hot Caro's acid mixture exits the reactor unit. In the case of treating precious metal tailings slurry to reduce their cyanide values (CN ), Caro's acid is added directly from the reactor to 30 the tailings slurry. The Caro's acid mist is released as the Caro's acid mixture free falls between the end of the Caro's acid reactor and the surface of the tailings slurry. Further, mist is released as the Caro's acid spreads outonto the surface of the slurry before it mixes with the tailings slurry. The higher the Caro's acid tel"perdl~re, the more acid mist is generated. Mixing 3s of the Caro's acid with the tailing slurry is not instantaneous due to the syrupy nature of the cGncent.dted Caro s acid and the high density of the tailings slurry (35% - 40% solids). The temperature of the tailing slurry also can affect the amount of acid mist generdted. Warm or hot slurry will conl,ibute to more mist than slurry at ambient te".pe,dl.Jres. The Caro s acid mist thus s generated can be particularly objsvtiol)able if the Caro s acid is employed indoors, where acid mist can build up. At some gold mines the tailing sump a CGIlllllOn i"je_tio,) point for Caro s acid to control the cyanide CGnCel llraliGnS of the tailings slurry is locAte-J i. .JoGr~. The acid mist has a sharp odor which can cause irritation of the mucus membranes. The acid 10 mist is also cG"~,sive to equipment and instruments used in precious metal recovery sites. Where the injection point for Caro s acid to a tailings pond is locAtecl outdoors, the Caro's acid mist is exl-~l"ely objectionable to anyone downwind from the site where the mist is generated.
In accordance with the present invention the Caro s acid mist can be lS subst~ntially reduced or even eliminated by quenching the hot Caro s acid mixture with water to both cool and dilute the mixture as it exits the Caro's acid reactor. The above quenching of the above hot Caro s acid mixture can take place in a number of ways. One way is to direct water sprays at the base of the pipe where the Caro s acid mixture exits. The water sprays 20 simultaneously emit water streams directly into the Caro s acid mixture and also form a curtain of water droplets that surround the end of the pipe from which the Caro s acid mixture exits. A second ",ell,od for carrying out the above quenching of the Caro s acid mixture is to introduce dilution water into an annular tube surrounding the outside of the pipe from which the Caro's 25 acid mixture exits resulting in a ring of water flowing co-currently with theCaro s acid contained within the water ring. The Caro's acid and water i"li".alely mix as they fall from the exit pipe of the Caro's acid reactor and the ring of water prevents any release of the Caro s acid mist before it is scrubbed and reacts with the water to quench and dilute the Caro s acid.
Another system for quenching the Caro's acid mixture is to attach a water aspirator to the pipe from which the Caro s acid mixture exits. As the Caro s acid mixture exits from the pipe water will be aspi, dted into the mixture, mixed with the Caro's acid and both cool and dilute the Caro s acid before it exits the aspirator pipe. Another allel"ate technique for quenching 35 the hot Caro's acid mixture is to attach a static mixer to the exit pipe of the Caro's acid reactor wherein water and the Caro's acid mixture are passed simultaneously into the static mixture in order to quench the Caro's acid. The static mixer is a desirable ,nell,od of carrying out the quenching operation bec~use it allows i"li",ate contact of the Caro's acid and water 5 simultaneously and with varying amounts of water as desired. The instant mixing of the water and Caro's acid assures immediate dilution and cooling of the Caro's acid before it exits from the static mixer into the tailings sump.
Finally, the simplest and most economic way of carrying out the quenching of the Caro's acid mixture is to place the exit tube of the Caro's acid reactor into 10 a container in which a continuous water stream is directed with the exit tubebeing below the level of the water that is present in the container. In other words the exit tube is placed into a container full of water, below the water level, and into which a continuous water stream is directed and overflows the container. In this way there is instantaneous quenchi"g of the Caro's 15 acid mixture as it exits the tube into the container of water and the constant supply of water into the container results in overflowing a diluted Caro's acid mixture from the container into the tailings pond. Since the exit pipe from the Caro's acid reactor is below the water level in the container no mist or Caro's acid solution can esc~pe from the tube without first contacting and being 20 quenched and cooled by water which is in the container. Thus, both quenchi, ,9, that is cooling of the Caro's acid mixture, is obtained along with simultaneous dilution.
The amount of water employed for water dilution and quenching is not critical and can vary widely. For example we have found that from 1/1 to 25 200/1 weight dilution of water to Caro's acid is effective. Obviously, largeramounts of water can be used without del~terious affects. The dilution water can be at any temperature which will cool the Caro's acid mixture.
Temperatures from about 5Q to about 45~C are useful with ambient te"".6rdlures being preferred bec~use they are the most economical. Since 30 the temperature of the Caro's acid mixture exiting from the Caro's acid reactor is nommally from about 52~C to 98QC, any temperature below 52~C will usually be effective. Obviously the lower the temperature of the dilution water the more effective will be the results since it will minimize cJecGn,posilion and hydrolysis of the Caro's acid.
At an eA~eri",e"tal test site where the invention was ~,"Jer~o..lg testing an unusual event u"ex~ecte-lly allowed the evaluation of the invention in a visual mode. The testing was carried out with a tailing slurry recovered from a gold extraction using sodium cyanide as the extracting 5 agent. In this case the Caro's acid is employed to reduce the cyanide levels in the tailings slurry. In the first instance the Caro's acid was added to the tailing slurry without any water to quench the Caro's acid mixture. The Caro's acid mixture exited from the outlet pipe of a static Caro's acid reactor several inches above the tailing slurry pond and dropped into the tailing 10 slurry. The tailing slurry in contact with undiluted Caro's acid tumed green. It is believed that the green color was due to some co""~onent of the ore slurry such as a heavy metal changing color under oxkl;;liol) and/or acid conditions.
Once the Caro's acid mixed with the slurry the green color ~is~ppe~red.
Thus, the green color provided a unique visual opportunity to observe mixing 15 pattems of Caro's acid with the slurry and to observe any unreacted Caro's acid which was green in color and which floated on top of the tailing slurry. Inthe absence of water quenching and dilution, a mist formed around the outlet pipe and scattered pools of Caro's acid could be observed, green in color, floating on top of the wamm slurry (containing 37 weight percent solids) and 20 could be seen bubbling (dec~""~osi"g) and el"illi"y an acid mist prior to disappearing into the slurry. Also, green streaks were also seen at the surface of the slurry at a slurry outlet pipe loc~ted downstream about 12 feet from the Caro's acid injection point. After water quenching and dilution of the Caro's acid mixture exiting from the outlet pipe, the pools of Caro's acid 25 floating on the slurry were much smaller, disappearing very quickly, and the bubbling previously seen in the aL,sence of water dilution was absent. In addition no green streaks were cviJel ,t at the slurry pipe outlet 12 feet dGw"~l,eam from the Caro's acid ~ddition point. The mixing of the Caro's acid into the slurry was due to the thinning effect of the water on the Caro's 30 acid. The water quel)cl ,ing and dilution of the Caro's acid eliminated the acid mist and improved mixing of the Caro's acid due to the cooling and thinning - effect of the added water.
While an important use of the invention is the ~pplic~liGIl of Caro's acid for detoxification of cyanides (CN-) and WAD (Weekly Acid Dissociable) 35 CN in gold mine tailings slurries, the invention can also be used in any other application where Caro's acid is prepared on site and injected into a sul,str~te to destroy, deodorize, decolor, or alter a chemical comrosition.
Among such applications is the delignificaliGn of wood pulp, phenol destruction and de~olo,iLali~,) and cleodo,i~dlioll of a wide variety of waste s water solutions and slurries.
By carrying out the ~.rese!nt process of quenching the hot Caro's acid mixture before using the Caro's acid to treat tailing slurry for reduction of their cyanide concenl~alions, it has been found that the efficiency of cyanide destruction is materially i"creased without increasing the amount of Caro's 10 acid used in the process. This additional benefit of using the instant quenching operation results bec~use of two separate actions that take place when the Caro's acid is quencl ,ed. Initially the Caro's acid is rapidly cooled by the quenching step and this prevents rapid decGmpositiGI ~ of the hot Caro's acid with the loss of oxidizing potential. In addition the water dilutes 15 the Caro's acid considerably and makes it a much thinner solution than the viscous mixture that exits from the Caro's acid reactor. This is important bec~llse when this Caro's acid mixture is added to the viscous tailing slurry the diluted Caro's acid which has much less viscosity can readily mix with the tailing slurry as compared with the more syrupy viscous Caro's acid which is undiluted. The faster mixing diluted Caro's acid can thus react quickly with the cyanide values in the tailing slurry and thereby reduce decG",position of Caro's acid from unmixed pools of Caro's acid floating on top of the tailing slurry. By CGIItldSt, when the Caro's acid is not diluted, the syrupy Caro's acid mixture exiting from the Caro's acid reactor fomms many large pools on the surface of the tailing slurry and these pools can be seen to be bubbling indicating that the hot Caro's acid is decGI"posing. This is wasteful of oxidizing potential of the Caro's acid and of course, dil"inishes the effectiveness of the Caro's acid in reducing the cyanide concel,l.dlion in the tailing slurry. By quenching the Caro's acid mixture as it issues from the 30 Caro's acid reactor, decomposition of the hot Caro's acid is eliminated by cooli"y it and the now thinned Caro's acid can more readily react and mix - with the tailing slurry without first being subjected to decor,~positiGn before it mixes and reacts with the cyanide in the tailing slurry. This was completely unexpected and is an additional bonus of the pr~cess along with elimination 35 or reduction of the Caro's acid mist.
The following are exal"pl~s which illustrate the use of the present process.
Example 1 Generation and Use of Caro s Acid Without Water ~uenching-Prior Art sA Caro s acid generator co"sisli"g of a funneling zone attached to a static tubular reactor inst~l'ecl in a vertical position beneath the funneling zone and containing four (4) mixing elen,e"ls was placed over a sump filled with tailing slurry that contained residual cyanide values. The funneling zone was open to the atmosphere as was the outlet of the static reactor. Sulfuric 10 acid in the amount of 0.85 gallons per minute of 93% by weight H2SO4 and 0.20 gallons per minute of 70 weight ~,ercent of H2O2 was added to the funneling zone and produced from the bottom of the reactor a mixture containing 27% Caro s acid on a continuous basis. The Caro's acid mixture was passed directly into the sump to treat a stream of 840 gallons per minute 15 of the tailing slurry containing 1.3 Ibs. per minute of cyanide (CN ). This equated to a Caro s acid/cyanide mole ratio of 0.71/1 and res~lted in a 43.3%
destruction of WAD cyanide (CN ). The hot Caro s acid exiting from the Caro s acid generator was not treated in any way before it fell into the sump containing the tailing slurry. Caro s acid mist was prevalent in the vicinity of20 the Caro's acid addition point.
Generation and Use of Caro s Acid with Water Quenching-lnventive Process The same eqL;,~r"ent and reagents were used as in the example above except that the 840 gallons per minute of tailing slurry contained 1.5 Ibs. per minute of cyanide (CN-) and this was t,eat~d with the Caro s acid 2s prepared from 1.0 gallon per minute of 93% sulfuric acid and 0.25 gallons perminute of 70% hydrogen peroxide (all weight percent). This equated to a cyanuric acid/cyanide mole ratio of 0.64/1 and resulted in a 68% destruction of WAD cyanide (CN ). During this run a spray of water was directed towards the end of Caro s acid outlet pipe so that it impinged directly on the hot 30 Caro's acid mixture exiting from the Caro's acid reactor. The water was at ambient temperature and the amount of water used was estimated to be in excess of a weight ratio of water to Caro s acid of 10:1. There was no detectable Caro s acid mist pres6nl in the vicinity of the Caro s acid outlet pipe. For a brief time during the trial the water that was being sprayed on the 3s outlet pipe was shut off and shortly thereafter the acid mist retumed W O 97/00225 PCTrUS96/10475 i"""ediately. When the water was tumed on again, allowing the water spray to impinge upon the outlet of the Caro's acid pipe, the acid mist quickly disappeared.
Example 2 Another run was made using the same Caro's acid generator and reagents as in Example 1, except that the 840 gallons per minute of tailing slurry contained 1.8 Ibs/minute of cyanide values (CN-) and was l~ated with Caro's acid prepared from 1.0 gallons per minute of 93% by weight H2SO4 and 0.25 gallons per minute of 70% by weight H2O2. This equated to a Caro's acid/cyanide mole ratio of 0.64/1 and resulted in a 50% destruction of WAD cyanide (CN-). During this run a large plastic bucket was positioned under the Caro's acid outlet pipe and a stream of water was continually added to the bucket. The level of the Caro's acid outlet pipe was below the water level in the bucket and the Caro's acid and water mixture in the bucket overflowed into the tailings slurry contained below it. No Caro's acid mist was present and no bubbling of any pockets of Caro's acid pools floating on top of the slurry were observable in the vicinity of the Caro's acid injection point. Also no green streaks were evident on the surface of the tailings slurry in the slurry pipe outlet 12 feet downstream from the Caro's acid injection point. By contrast, when the Caro's acid was pellllitled to flow directly into the tailing slurry without being quenched with water, pools of Caro's acid which were green colored floated on top of the slurry and were seen to be bubbling indicating Caro's acid decG"" osi"y. Further green sl,eaks were evident at the slurry pipe outlet 12 feet downstream from the Caro's acid injection point and there was subst~ntial Caro's acid mist surrounding the area where the outlet pipe from the Caro's acid generator fed the hot Caro's acid mixture to the tailing slurry.
The invention is in the field of producing Caro's acid by reaction of s hydr~gen peroxide and sulfuric acid in a controlled and effective manner.
Caro s acid which is peroxymonosulfuric acid is a strong oxidi~i, ,9 cor"pound which has been suy~ested for use in any applicdlions including pulificalion of cyanide-containing effluents by conversion of their cyanides into non-toxic derivatives. Caro's acid is usually produced by reacting togetl,er cGr,cenl,dted sulfuric acid (85% to 98% by weight H2SO~) with cGncentrated hydrogen peroxide (50% to 90% by weight H2O2) to produce an equilibrium mixture of Caro's acid containing peroxy",onosulfuric acid (H2SOs), sulfuric acid and hyd,ogen peroxide. I lov:ever, since the Caro s acid is not stable for long periGJs it must be made and imme~ tely used on site or quickly cooled and stored at refrigerated te",per~lures. In general, theCaro's acid is manufactured on site as needed and in just the amounts required for the specified ap~l c~tion without the necessity of having to store any excess amounts.
One procedure for producing Caro s acid is set forth in U.S. Patent No.
3 900 555 by using an apparatus descril,ed in U.S. Patent No. 3,939 072 for mixing the sulfuric acid and hydlogen peroxide and cooling the mixture with a water-cooled jacket to prevent overhearing of the reactants and premature clecGI~position of the monoperoxysulfuric acid product. These ~,atents teach the use of the monoperoxysulfuric acid product for treating waste aqueous effluents from an electroplating plant containing cyanide ions while simultaneously adding an alkali in amounts suitable for neutralizing the added acid. This assures that the pH of the treated solution in maintained at a specified alkaline value, nommally pH 9, by neutralizing any acidity resultingfrom the added acid.
Another procedure is set forth in U.S. Patent No. 4 915 849 wherein the Caro s acid is used to treat cyanide-containing effluents from an ore-p.ocessing plant. The Caro s acid is manufactured by reacting sulfuric acid with hydrosJen peroxide in propo,liGns cor,espol-ding to between 0.01 and 0.5 moles of sulfuric acid per mole of hydrogel) peroxide. The resulting acid is then added to the cyanide-containing effluent simultaneous with aqueous lime or sodium hydroxide mixtures in order to maintain the effluent at the preferred pH of between 9.5 and 11.5.
Still another procedure is set forth in PCT Publication No. WO
92/07791, a published patent ~pplic~tion of Lane et al., which teaches s production of peroxy.,.Gnosulfuric acid by introducing a hyd~ùgen peroxide solution into a stream of sulfuric acid ~lu~:;, ~y through a reaction chamber, the HzO2 intro~luction being made between the sulfuric acid inlet and the reaction mixture outlet. Both the hyd~ùgen peroxide solution and sulfuric acid are introduced under pressure into the closed tubular reaction cl ,aml,er of the invention. In the reaction, chamber, the through-put per minute of the reaction chamber is at least about 20 times its intemal volume measured b~l~con the inlet for the hyd~oge" peroxide and the outlet.
In carrying out the production of Caro's acid in industrial ~pl)lic~lions, two prùble."s have arisen in the scale-up of the Caro's acid generating unit to commercial proportions. The first prùble." is the protection of a large amount of hyd~os;en peroxide in storage tanks, used to feed the Caro's acid producing generator, from possible conta"-i.,ation. The need to prevent contamination of this large hydloyel1 peroxide source from either Caro's acid, sulfuric acid, or other such impurities is critical to the safe containment and use of the hy.l.ogen peroxide. The second problem is to control the Caro's acid reaction so that the Caro's acid is folllled efficiently with maximum use of the hydloyen peroxide reagent and without having the hot reaction mixtur formed during the reaction go out of control and overflow or rupture the reaction chamber.
2s With respect to the first problem, it has been the custom in the industry to isolate the storage tank of peroxide from the reactor where Caro's acid is pro~!lce-l by means of an intermediate tank (sG"-eli",es called a "break"
tank) to interrupt the stored hydroyel, peroxide source from the line deliveringhydrogen peroxide to the Caro's acid generator. The peroxide from the storage tank is passed by pump means or by gravity into the top of an intemnediate tank to a given level in the intermediate tank without requiring a direct liquid connection b~t~Joon the perùxide in the intermediate tank and the line flowing from the storage tank. This assures that any possible contamination which may be sucked back from the Caro's acid generator into the i"te""eJiate tank will not be able to flow into the hy.J,uyel) peroxide storage tank.
The secG"d problem arises bec~l~se the reaction of sulfuric acid and hyJu~gen peroxide is an exothemmic reaction and some h~,d~oyell peroxide JecGI"poses to fomm large amounts of gas which may cause pressure build up capable of rupturing the reactor or causing the reagents to overflow. This may cause the hot reaction mixture to go out of control with the waste of both sulfuric acid and hydrogen peroxide and further, if no break tank is used, may become a possiblE source of conta",i"alion of the hyJ,ugen peroxide storage 10 tank if it backs up into the hyclrogen peroxide line conl-e~;ti,-3 the hydroyell peroxide storage tank to the Caro's acid reactor.
In copending U.S. Application Serial No. 08/351 987 filed Decer,lber 8 1994, (now Patent No. 5 470,564) in the names of James L. Manganaro et al. a process is described that overcomes the fore~oi. ~y problems. This process for producing Caro's acid is carried out by reacting sulfuric acid having an cGncel llraliGn of at least about 85% by weight and hydrogen peroxide having a cGncenl~dlion of at least about 50% by weight wherein the hydrogen peroxide is introduced through a first feed line and the sulfuric acid is introduced through a second feed line into a funneling zone open to the atmosphere, the first feed line and secGn d feed line having air gaps between their ends and the funneling zone, passing said hyd-ogen peroxide and sulfuric acid by gravity flow from said funneling zone into one end of a reaction zone that has been sized to permit a pressure drop therein which is at least 8 times the theoretical pressure drop for liquids flowing through such reaction zone and removing a mixture containing Caro's acid from an exit end of the reaction zone.
While the above process has been very suGcessful in eliminating the need for break tanks and avoiding pressure buildups in the reactor, the Caro s acid that issues from the end of the reactor open to the atmosphere is quite hot bec~use of the exothemmic reaction between the sulfuric acid and h~,J,ogen peroxide and tends to form an undesiled Caro s acid mist. The Caro's acid mist is an irritant to the mucus ",eull,ranes of workers who are in the vicinity of the outlet of the Caro s acid reactor. The mist is especially objectionable when the reactor is inside a building where the mist can collect and build up in conce"lf~lion to a point where protective gear and/or special W O 97/00225 PCTrUS96/10475 exhaust provisions are required. Even outdoors the mist is notice~hlQ and most objectionable to any workmen who may be downwind from the Caro's acid reactor. Further, when the Caro's acid is used to treat tailing slurries toreduce their cyanide conce"l,dlions, the mixing of the Caro's acid with the tailing slurries is not instanlaneous due to the syrupy nature of the COI Ice, Itrdl6cl Caro's acid that issues from the Caro's acid generator and thehigh density of the tailing slurries (35% to 40% solids). This is undesired bec~l ~se it allows time for the Caro's acid to decompose before reacting with the cyanide in the tailing slurry.
It has now been found that the Caro's acid mist, that fomms when Caro's acid is produced by reaction of sulfuric acid and hyd~ogen peroxide in a reaction zone and the hot Caro's acid mixture is released from the end of the reaction zone, can be reduced or eliminated by quenchi. ,9 the hot Caro's acid mixture with water to both cool and dilute the Caro's acid.
In carrying out the present invention, the Caro's acid is produced by reacting sulfuric acid and hydrogen peroxide together, preferably in a continuous manner and in accordance with the process set forth in our copending U.S. Ar, '.c~tion SN 08/351,987filed Dece"lber8, 1994 (now Patent No. 5,470,564) in the names of James L. Manganaro et. al. While other processes may also be employed for producing the Caro's acid, this is the preferred method bec~l~se the Caro's acid is for",eJ efficial,lly with maximum use of hyclrogel) peroxide reagent and without having the hot reaction mixture fommed during the reaction go out of control and overflow or rupture the reaction chamber. In this process the reactants are added into a funneling zone, or other type of feeding zone, open to the alrnosphere and then the hydrogen peroxide and sulfuric acid flow from the funneling zone by gravity into one end of a reaction zone where the reaction takes place. The reaction zone which is loc~ted downstream from the funneling zone is preferably a pipe-like or tube reactor, whose diameter may be variable or constant, which may be either vertically oriented or h~ri~o,ltally oriented or any skew angle intermediate these two extremes and is fed by gravity from the funneling zone. Further, it is preferred that the reaction zone have a size which pemmits a pressure drop in the reaction zone which is at least eight times the theoretical pressure drop for liquids passing through such reaction zone. Such reaction zones are nommally static reactors containing several mixing elements which ensure a complete mixing and reaction of the two reagents.
The sulfuric acid employed in the reaction can be of any c~r,ce, ll-dliO"
from about 85% by weight to about 98% by weight H2SO4 with about 93% by s weight sulfuric acid being preferred bec~use of its ready availability and workability. The hydr~gen peroxide employed can be of any conce"l,dlio from about 50% by weight H202 to about 90% by weight H202 with 70% by weight hyd~oyel, peroxide being ~,refer,tzd bec~use of safety considerations and availability. The mole ratios of sulfuric acid to hydr~yel, peroxide lo (H2SO4/H202) can range from about 1/1 to about 4/1 with about 2/1 to about 3/1 being prefe~.ed. The reaction results in Caro's acid being formed in a solution which is an equilibrium mixture of hydrogen peroxide, sulfuric acid, Caro's acid and water. The equation for this reaction is set forth below:
H2S~4 + H2~2 ~ H2SOs + H20 A typical cGl"~,osilion prepared from a 2.5/1 mole ratio of 93 weight percel ,l sulfuric acid and 70 weight percent hydrogel) peroxide is as follows:
Caro's Acid (peroxymonosulfuric acid) 25 weight percent; sulfuric acid 57 weight percent; hydrogel) peroxide 3.5 weight percent; and water 14.5 weight percel,t. A cG"si~lerable amount of heat is rcloascd as a result of mixing the hydrogen peroxide with sulfuric acid. The amount of heat rel ~ced depends on the concenlrdliGI) of the starting reagents and the mole ratios of sulfuric acid to hydrogen peroxide. Using the preferred cGncenlrdliol)s of 70 weight percent H202 and 93 weight percent H2SO4 and a preferred mole ratio of H2SO4/H202 of 2.5/1, an increase in te.n~.eralure of 58QC will occur. If, for example, the raw materials are at 34~C, the Caro's acid will reach a temperature of 92~C.
Caro's acid mist is generated as the hot Caro's acid mixture exits the reactor unit. In the case of treating precious metal tailings slurry to reduce their cyanide values (CN ), Caro's acid is added directly from the reactor to 30 the tailings slurry. The Caro's acid mist is released as the Caro's acid mixture free falls between the end of the Caro's acid reactor and the surface of the tailings slurry. Further, mist is released as the Caro's acid spreads outonto the surface of the slurry before it mixes with the tailings slurry. The higher the Caro's acid tel"perdl~re, the more acid mist is generated. Mixing 3s of the Caro's acid with the tailing slurry is not instantaneous due to the syrupy nature of the cGncent.dted Caro s acid and the high density of the tailings slurry (35% - 40% solids). The temperature of the tailing slurry also can affect the amount of acid mist generdted. Warm or hot slurry will conl,ibute to more mist than slurry at ambient te".pe,dl.Jres. The Caro s acid mist thus s generated can be particularly objsvtiol)able if the Caro s acid is employed indoors, where acid mist can build up. At some gold mines the tailing sump a CGIlllllOn i"je_tio,) point for Caro s acid to control the cyanide CGnCel llraliGnS of the tailings slurry is locAte-J i. .JoGr~. The acid mist has a sharp odor which can cause irritation of the mucus membranes. The acid 10 mist is also cG"~,sive to equipment and instruments used in precious metal recovery sites. Where the injection point for Caro s acid to a tailings pond is locAtecl outdoors, the Caro's acid mist is exl-~l"ely objectionable to anyone downwind from the site where the mist is generated.
In accordance with the present invention the Caro s acid mist can be lS subst~ntially reduced or even eliminated by quenching the hot Caro s acid mixture with water to both cool and dilute the mixture as it exits the Caro's acid reactor. The above quenching of the above hot Caro s acid mixture can take place in a number of ways. One way is to direct water sprays at the base of the pipe where the Caro s acid mixture exits. The water sprays 20 simultaneously emit water streams directly into the Caro s acid mixture and also form a curtain of water droplets that surround the end of the pipe from which the Caro s acid mixture exits. A second ",ell,od for carrying out the above quenching of the Caro s acid mixture is to introduce dilution water into an annular tube surrounding the outside of the pipe from which the Caro's 25 acid mixture exits resulting in a ring of water flowing co-currently with theCaro s acid contained within the water ring. The Caro's acid and water i"li".alely mix as they fall from the exit pipe of the Caro's acid reactor and the ring of water prevents any release of the Caro s acid mist before it is scrubbed and reacts with the water to quench and dilute the Caro s acid.
Another system for quenching the Caro's acid mixture is to attach a water aspirator to the pipe from which the Caro s acid mixture exits. As the Caro s acid mixture exits from the pipe water will be aspi, dted into the mixture, mixed with the Caro's acid and both cool and dilute the Caro s acid before it exits the aspirator pipe. Another allel"ate technique for quenching 35 the hot Caro's acid mixture is to attach a static mixer to the exit pipe of the Caro's acid reactor wherein water and the Caro's acid mixture are passed simultaneously into the static mixture in order to quench the Caro's acid. The static mixer is a desirable ,nell,od of carrying out the quenching operation bec~use it allows i"li",ate contact of the Caro's acid and water 5 simultaneously and with varying amounts of water as desired. The instant mixing of the water and Caro's acid assures immediate dilution and cooling of the Caro's acid before it exits from the static mixer into the tailings sump.
Finally, the simplest and most economic way of carrying out the quenching of the Caro's acid mixture is to place the exit tube of the Caro's acid reactor into 10 a container in which a continuous water stream is directed with the exit tubebeing below the level of the water that is present in the container. In other words the exit tube is placed into a container full of water, below the water level, and into which a continuous water stream is directed and overflows the container. In this way there is instantaneous quenchi"g of the Caro's 15 acid mixture as it exits the tube into the container of water and the constant supply of water into the container results in overflowing a diluted Caro's acid mixture from the container into the tailings pond. Since the exit pipe from the Caro's acid reactor is below the water level in the container no mist or Caro's acid solution can esc~pe from the tube without first contacting and being 20 quenched and cooled by water which is in the container. Thus, both quenchi, ,9, that is cooling of the Caro's acid mixture, is obtained along with simultaneous dilution.
The amount of water employed for water dilution and quenching is not critical and can vary widely. For example we have found that from 1/1 to 25 200/1 weight dilution of water to Caro's acid is effective. Obviously, largeramounts of water can be used without del~terious affects. The dilution water can be at any temperature which will cool the Caro's acid mixture.
Temperatures from about 5Q to about 45~C are useful with ambient te"".6rdlures being preferred bec~use they are the most economical. Since 30 the temperature of the Caro's acid mixture exiting from the Caro's acid reactor is nommally from about 52~C to 98QC, any temperature below 52~C will usually be effective. Obviously the lower the temperature of the dilution water the more effective will be the results since it will minimize cJecGn,posilion and hydrolysis of the Caro's acid.
At an eA~eri",e"tal test site where the invention was ~,"Jer~o..lg testing an unusual event u"ex~ecte-lly allowed the evaluation of the invention in a visual mode. The testing was carried out with a tailing slurry recovered from a gold extraction using sodium cyanide as the extracting 5 agent. In this case the Caro's acid is employed to reduce the cyanide levels in the tailings slurry. In the first instance the Caro's acid was added to the tailing slurry without any water to quench the Caro's acid mixture. The Caro's acid mixture exited from the outlet pipe of a static Caro's acid reactor several inches above the tailing slurry pond and dropped into the tailing 10 slurry. The tailing slurry in contact with undiluted Caro's acid tumed green. It is believed that the green color was due to some co""~onent of the ore slurry such as a heavy metal changing color under oxkl;;liol) and/or acid conditions.
Once the Caro's acid mixed with the slurry the green color ~is~ppe~red.
Thus, the green color provided a unique visual opportunity to observe mixing 15 pattems of Caro's acid with the slurry and to observe any unreacted Caro's acid which was green in color and which floated on top of the tailing slurry. Inthe absence of water quenching and dilution, a mist formed around the outlet pipe and scattered pools of Caro's acid could be observed, green in color, floating on top of the wamm slurry (containing 37 weight percent solids) and 20 could be seen bubbling (dec~""~osi"g) and el"illi"y an acid mist prior to disappearing into the slurry. Also, green streaks were also seen at the surface of the slurry at a slurry outlet pipe loc~ted downstream about 12 feet from the Caro's acid injection point. After water quenching and dilution of the Caro's acid mixture exiting from the outlet pipe, the pools of Caro's acid 25 floating on the slurry were much smaller, disappearing very quickly, and the bubbling previously seen in the aL,sence of water dilution was absent. In addition no green streaks were cviJel ,t at the slurry pipe outlet 12 feet dGw"~l,eam from the Caro's acid ~ddition point. The mixing of the Caro's acid into the slurry was due to the thinning effect of the water on the Caro's 30 acid. The water quel)cl ,ing and dilution of the Caro's acid eliminated the acid mist and improved mixing of the Caro's acid due to the cooling and thinning - effect of the added water.
While an important use of the invention is the ~pplic~liGIl of Caro's acid for detoxification of cyanides (CN-) and WAD (Weekly Acid Dissociable) 35 CN in gold mine tailings slurries, the invention can also be used in any other application where Caro's acid is prepared on site and injected into a sul,str~te to destroy, deodorize, decolor, or alter a chemical comrosition.
Among such applications is the delignificaliGn of wood pulp, phenol destruction and de~olo,iLali~,) and cleodo,i~dlioll of a wide variety of waste s water solutions and slurries.
By carrying out the ~.rese!nt process of quenching the hot Caro's acid mixture before using the Caro's acid to treat tailing slurry for reduction of their cyanide concenl~alions, it has been found that the efficiency of cyanide destruction is materially i"creased without increasing the amount of Caro's 10 acid used in the process. This additional benefit of using the instant quenching operation results bec~use of two separate actions that take place when the Caro's acid is quencl ,ed. Initially the Caro's acid is rapidly cooled by the quenching step and this prevents rapid decGmpositiGI ~ of the hot Caro's acid with the loss of oxidizing potential. In addition the water dilutes 15 the Caro's acid considerably and makes it a much thinner solution than the viscous mixture that exits from the Caro's acid reactor. This is important bec~llse when this Caro's acid mixture is added to the viscous tailing slurry the diluted Caro's acid which has much less viscosity can readily mix with the tailing slurry as compared with the more syrupy viscous Caro's acid which is undiluted. The faster mixing diluted Caro's acid can thus react quickly with the cyanide values in the tailing slurry and thereby reduce decG",position of Caro's acid from unmixed pools of Caro's acid floating on top of the tailing slurry. By CGIItldSt, when the Caro's acid is not diluted, the syrupy Caro's acid mixture exiting from the Caro's acid reactor fomms many large pools on the surface of the tailing slurry and these pools can be seen to be bubbling indicating that the hot Caro's acid is decGI"posing. This is wasteful of oxidizing potential of the Caro's acid and of course, dil"inishes the effectiveness of the Caro's acid in reducing the cyanide concel,l.dlion in the tailing slurry. By quenching the Caro's acid mixture as it issues from the 30 Caro's acid reactor, decomposition of the hot Caro's acid is eliminated by cooli"y it and the now thinned Caro's acid can more readily react and mix - with the tailing slurry without first being subjected to decor,~positiGn before it mixes and reacts with the cyanide in the tailing slurry. This was completely unexpected and is an additional bonus of the pr~cess along with elimination 35 or reduction of the Caro's acid mist.
The following are exal"pl~s which illustrate the use of the present process.
Example 1 Generation and Use of Caro s Acid Without Water ~uenching-Prior Art sA Caro s acid generator co"sisli"g of a funneling zone attached to a static tubular reactor inst~l'ecl in a vertical position beneath the funneling zone and containing four (4) mixing elen,e"ls was placed over a sump filled with tailing slurry that contained residual cyanide values. The funneling zone was open to the atmosphere as was the outlet of the static reactor. Sulfuric 10 acid in the amount of 0.85 gallons per minute of 93% by weight H2SO4 and 0.20 gallons per minute of 70 weight ~,ercent of H2O2 was added to the funneling zone and produced from the bottom of the reactor a mixture containing 27% Caro s acid on a continuous basis. The Caro's acid mixture was passed directly into the sump to treat a stream of 840 gallons per minute 15 of the tailing slurry containing 1.3 Ibs. per minute of cyanide (CN ). This equated to a Caro s acid/cyanide mole ratio of 0.71/1 and res~lted in a 43.3%
destruction of WAD cyanide (CN ). The hot Caro s acid exiting from the Caro s acid generator was not treated in any way before it fell into the sump containing the tailing slurry. Caro s acid mist was prevalent in the vicinity of20 the Caro's acid addition point.
Generation and Use of Caro s Acid with Water Quenching-lnventive Process The same eqL;,~r"ent and reagents were used as in the example above except that the 840 gallons per minute of tailing slurry contained 1.5 Ibs. per minute of cyanide (CN-) and this was t,eat~d with the Caro s acid 2s prepared from 1.0 gallon per minute of 93% sulfuric acid and 0.25 gallons perminute of 70% hydrogen peroxide (all weight percent). This equated to a cyanuric acid/cyanide mole ratio of 0.64/1 and resulted in a 68% destruction of WAD cyanide (CN ). During this run a spray of water was directed towards the end of Caro s acid outlet pipe so that it impinged directly on the hot 30 Caro's acid mixture exiting from the Caro's acid reactor. The water was at ambient temperature and the amount of water used was estimated to be in excess of a weight ratio of water to Caro s acid of 10:1. There was no detectable Caro s acid mist pres6nl in the vicinity of the Caro s acid outlet pipe. For a brief time during the trial the water that was being sprayed on the 3s outlet pipe was shut off and shortly thereafter the acid mist retumed W O 97/00225 PCTrUS96/10475 i"""ediately. When the water was tumed on again, allowing the water spray to impinge upon the outlet of the Caro's acid pipe, the acid mist quickly disappeared.
Example 2 Another run was made using the same Caro's acid generator and reagents as in Example 1, except that the 840 gallons per minute of tailing slurry contained 1.8 Ibs/minute of cyanide values (CN-) and was l~ated with Caro's acid prepared from 1.0 gallons per minute of 93% by weight H2SO4 and 0.25 gallons per minute of 70% by weight H2O2. This equated to a Caro's acid/cyanide mole ratio of 0.64/1 and resulted in a 50% destruction of WAD cyanide (CN-). During this run a large plastic bucket was positioned under the Caro's acid outlet pipe and a stream of water was continually added to the bucket. The level of the Caro's acid outlet pipe was below the water level in the bucket and the Caro's acid and water mixture in the bucket overflowed into the tailings slurry contained below it. No Caro's acid mist was present and no bubbling of any pockets of Caro's acid pools floating on top of the slurry were observable in the vicinity of the Caro's acid injection point. Also no green streaks were evident on the surface of the tailings slurry in the slurry pipe outlet 12 feet downstream from the Caro's acid injection point. By contrast, when the Caro's acid was pellllitled to flow directly into the tailing slurry without being quenched with water, pools of Caro's acid which were green colored floated on top of the slurry and were seen to be bubbling indicating Caro's acid decG"" osi"y. Further green sl,eaks were evident at the slurry pipe outlet 12 feet downstream from the Caro's acid injection point and there was subst~ntial Caro's acid mist surrounding the area where the outlet pipe from the Caro's acid generator fed the hot Caro's acid mixture to the tailing slurry.
Claims (11)
1. In the process of producing Caro's acid by reaction of sulfuric acid and hydrogen peroxide in a reaction zone to produce a hot Caro's acid mixture, and wherein the hot Caro's acid forms a mist of Caro's acid as it is released from the end of the reaction zone, the improvement characterized by quenching the hot Caro's acid mixture with water to both cool and dilute the Caro's acid thereby reducing or eliminating the Caro's acid mist.
2. Process of claim 1 characterized in that the sulfuric acid has a concentration of 85% to 98% by weight H2SO4.
3. Process of claim 1 characterized in that the sulfuric acid has a concentration of 93% by weight H2SO4.
4. Process of claim 1 characterized in that the hydrogen peroxide has a concentration of 50% to 90% by weight H2O2.
5. Process of claim 1 characterized in that the hydrogen peroxide has a concentration of 70% by weight H2O2.
6. Process of claim 1 characterized in that the mole ratio of H2SO4 to H2O2 employed is 1:1 to 4:1.
7. Process of claim 1 characterized in that the mole ratio of H2SO4 to H2O2 employed is 2:1 to 3:1.
8. Process of claim 1 characterized in that the reaction zone is a static tubular reaction zone.
9. Process of claim 1 characterized in that the water used for quenching the Caro's acid is employed in a water to Caro's acid weight ratio of 1:1 to 200:1.
10. Process of claim 1 characterized in that the water used for quenching the Caro's acid is at a temperature below 52°C.
11. Process of claim 1 characterized in that the water used for quenching the Caro's acid has a temperature of from 5°C to 45°C.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US49143995A | 1995-06-16 | 1995-06-16 | |
| US08/491,439 | 1995-06-16 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2224016A1 true CA2224016A1 (en) | 1997-01-03 |
Family
ID=23952232
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2224016 Abandoned CA2224016A1 (en) | 1995-06-16 | 1996-06-17 | Method for producing caro's acid |
Country Status (4)
| Country | Link |
|---|---|
| AU (1) | AU700876B2 (en) |
| BR (1) | BR9608341A (en) |
| CA (1) | CA2224016A1 (en) |
| WO (1) | WO1997000225A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2666413C (en) | 2006-10-18 | 2016-08-02 | Mitsubishi Gas Chemical Company, Inc. | Method for producing peroxymonosulfuric acid and apparatus for continuously producing peroxymonosulfuric acid |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB738407A (en) * | 1953-01-16 | 1955-10-12 | Stevensons Dyers Ltd | A process for the manufacture of permonosulphuric acid |
| US2789954A (en) * | 1953-12-14 | 1957-04-23 | Stevensons Dyers Ltd | Process for making peroxymonosulphuric acid |
| GB9023433D0 (en) * | 1990-10-27 | 1990-12-12 | Interox Chemicals Ltd | Peroxoacid manufacture |
| US5397482A (en) * | 1993-08-03 | 1995-03-14 | Fmc Corporation | Treatment of cyanides in effluents with Caro's acid |
| US5470564A (en) * | 1994-08-01 | 1995-11-28 | Fmc Corporation | Method for producing caro's acid |
-
1996
- 1996-06-17 CA CA 2224016 patent/CA2224016A1/en not_active Abandoned
- 1996-06-17 WO PCT/US1996/010475 patent/WO1997000225A1/en active Application Filing
- 1996-06-17 BR BR9608341A patent/BR9608341A/en not_active Application Discontinuation
- 1996-06-17 AU AU62824/96A patent/AU700876B2/en not_active Ceased
Also Published As
| Publication number | Publication date |
|---|---|
| WO1997000225A1 (en) | 1997-01-03 |
| AU700876B2 (en) | 1999-01-14 |
| AU6282496A (en) | 1997-01-15 |
| BR9608341A (en) | 1999-01-05 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4590057A (en) | Process for the generation of chlorine dioxide | |
| US4080428A (en) | Process for the purification of flue and other waste gas | |
| US5879653A (en) | Method for producing caro's acid | |
| RU2262982C2 (en) | Method and device for conducting reaction in liquid medium at liberation of gas | |
| US20120031158A1 (en) | Continuous process for preparation of calcium thiosulfate liquid solution | |
| US4724132A (en) | Continuous process for the manufacture of metal salt solutions from water-insoluble metal compounds and mineral acids | |
| KR100507598B1 (en) | Method for preventing scaling in wet-process waste gas treatment equipment | |
| US3256068A (en) | Apparatus for the production of silica pigments | |
| CA2224016A1 (en) | Method for producing caro's acid | |
| EP4188880A1 (en) | Method for manufacturing ammonium sulphate and calcium carbonate from phosphogypsum | |
| EP0514848A2 (en) | Process and apparatus for the generation of peroxyacids | |
| JP2009279567A (en) | Method and apparatus for treating exhaust gas containing chloropolysilane | |
| US3627676A (en) | Method for oxidizing the thiosulfate ions in a thiosulfate | |
| EA010599B1 (en) | Process for production of chlorine dioxide | |
| PL119292B1 (en) | Method of purification of phosphogypsum | |
| EP0153841A2 (en) | Production of chlorine dioxide | |
| MXPA97009964A (en) | Method to produce acid of c | |
| US8734739B2 (en) | Process for treating spent pickle liquor and/or ferrous chloride | |
| JPH1192104A (en) | High-purity chlorine dioxide aqueous composition, its production and producing device | |
| US4207201A (en) | Process for the manufacture of an aqueous iron (III)-chloride-sulfate solution | |
| CA2196533A1 (en) | Method for producing caro's acid | |
| AU2277400A (en) | Method, device and installation for continuously treating water | |
| CA2244223C (en) | Process for manufacturing caro's acid | |
| US4717429A (en) | Process for the removal of alkali metal nitrite from nitrate containing salt baths | |
| JPS5932993A (en) | Treatment of cyanide ion-contg. matter |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |