WO2002036839A1

WO2002036839A1 - Method and installation of metal retrieving from used chroming solutions

Info

Publication number: WO2002036839A1
Application number: PCT/RO2001/000017
Authority: WO
Inventors: Benedict Pisicescu; Petrisor Paul Lungulescu
Original assignee: Benedict Pisicescu; Petrisor Paul Lungulescu
Priority date: 2000-10-30
Filing date: 2001-09-25
Publication date: 2002-05-10
Also published as: AU2001290393A1; RO117687B1

Abstract

The invention concerns a method or procedure and an installation of metal retrieving from used water chroming solutions, with high content of Cr and other impurifying metals as Fe, Cr3+, Cu, using as reactive the gas ammonia, introducted at the base of the reaction tub, through a detachable device, connected to a gas contained through a flexible tube. The technology consists in the reduction of the acidity of the used solution, from PH = 0,5 to a PH of 5.5, in the same time with the precipitation of the impurifying metals as insoluble hydroxydes non toxic and re-usable, as well as the separation of the Cr6+ as water solution of ammonia dychromate.

Description

METHOD AND INSTALLATION OF METAL RETRIEVING FROM USED CHROMING SOLUTIONS

The invention concerns a method and an installation of retrieving metals after the neutralization of the used water chrossing solution, proceeded from the chroming bath of pieces made from ferrous or non-ferrous materials.

In the field of protection covering, place of it^s own is occupied by the functionnal and protecting - decorative depositions made by dure chroming. Daring the anodic attack of the pieces to he chromed into the solution are passing matalic ions from the superficial layed that can be iron,copper, zinc,nickel and others. Also in this solutions there are forming ions of C by reduction of Cr at the cathode. The iron and Cr in thiβ concentration improve the covering capacity of chroming solution. It has been proved that the sum of Fe -J- C must not exeed 20 g/L value over which the efficiency of the processes is decressing and the chroming solution is considered worn ou

There are methods of neutralisation and retrival of metals from a solution of chroming that is used,methods consisting either in the trea ment with reac ives of precipitation of Cr as insoluble chromats, using barium salts or lead salts,or the separation ©f Cr from the other metals with the help of the ion changer or by electro-dyalisis.

The drawbacks of these methods consist in the neutralization of the solution of chroming used in orCer to purify the residual waters to be eliminated.

In this manner, result abundant muds that imply either adequate storage or use of expensive toxic reactives, requesting precise dosing in order to avoid any excess.

There are also in use some installations of treating the water chroming solution consistiong in an umique vessel of neutralization wώthin the treating station of galvanic water.

The drawbacks of these installations consist in those that they are ment for the diluted water solutions, steo-chiometriyally treated after chemical analysis, ith a requirement of adequate space for waste deposit.

This technical obstacle our invention avoids consists in the retri eval from the water used chroming solutions of both the active metalic

6+ element that is Cr and the impure metalic elements.

Our technical procedure avoids the drawbacks hereby described by permitting the treatment of the water solution of chroming that has been used,containing Cr , Cr , Fe as other heavy impure metals as Zn, Cu,Cd, Ni,Al,came from the anodic attack of the pieces subject of the chroming process within environemental temperature - with gas ammonia 30 - 40 1/cm for a period of 1, - 1,5 Hours when the solution temperature reaches 75 - 80° Celsius resulting a water solution of ammonia di-chromate and metal precipitation under a form of insolvable hydroxides,not toxical and re-usable in the same time with the reaction of neutralization when the PH reaches 5,5 - 6.

The installation, accordind to the invention, leaves aside the draw' backs hereby mentioned by the detachable distributer made out of lead for gas Nh₃ placed inside and at the bottom of a tub, filled with used water solution,connected through a flexible tube to a gas bottle mounted on a carrige,with a electrochemical sensor of NH, as well as an aspiration pump to conduct the treated solution to a press-filter that separates the filtrated in a reservoir, nd the resulted precipitate is dry, calcinated and ground.

The procedure and the installation, according to the invention, show the next advantages : - permits the separate treatment of used chroming baths,

- permits the separation of the Cr from the solution

- permits the recovery of the impure metalic elements as insolvable products,non-toxic and re-usable.

- dos not require toxic waste space.

- the construction is relatively simple,

- does not present any toxic hazard to the operator,

- does not afect the environemtnt

We hereby give an example of realization of the procedure and the installation,according to the invention, connected to the drawing representing a scheme - view of the technological processus.

The method, according to the invention, consists in treatment of water chroming solution that has been used, with a content of 150-160 g/1 Cr⁶⁺, 15 - 20 g/1 Cr³⁺ ,15 - 20 g/1 Fe and PH of 0,5 - 0,7 places in a metalic tub, placked inside with lead with gAS AMMONIA WITHIN A PRESSURE OF MINIMUM ^■$& AT"* WITH A DEBIT OF 0,5 - 1 1 /min, The ammonia consumption has been 30-40 1 /m time of 1 - 1,5 h and the initial temperature of the solution has been that of the environe ment. and final temperature of 75 - 80° Celsius, with PH at 5,5 - 6

The gas ammonia is a concentrated reactive,very solvable,with great difuzion power in water solution and a basic characteristic, reason for which it is used for the neutralization of the used water solution of chroming.

In the first step, there are forming NH, OH according to the reac ic

NH₃ + H₂0 -* NH^ OH + Ql (1) that continues to react with the chromic acid according to reaction :

2HCrθ" j> Cr₂θ2" + HgO (2)

Cr₂0^~ + NhJoH^" ^(NH^)₂C ₂02- ^0H+ Q2 (3)

This way, with the formation of the ammonia dychromate, there is a incre« se of the PH value from 0,5 to 5.5 or 6. Both the solubilization of Ho and the reaction of the solution neutralization take place with great release of heat, reaching 75 - 80° Celsius,

In the second step of this processus, there is the reduction of the impure metals, consisting of Cr 3+ Fe and Cu and the birth of a insoluble hydroxide mud within ph from 2,5 to 5,5.

The reaching of PH value of 6 and the presence of H₃ at the surface of the solution indicates the termination of the reaction of neutralization and therefore cutting off the gas allimentation.

The excess of NH, has been avoided in order not to produce the solubilization of the precipitants formed as tetra amino-complexes and hexa aminoy complexes.

Further on the solution treated as mentioned, is filtered, with the separation of the solution of (NH, )Cr₂0.-, from the hydroxyde precipitat Cr(0H)₃, Fe(OH)₃,Cu(OH)₂.

The chemical analysis of the obtained filtrate has showed a con centration of : 195 -198 g/1 of Cr⁶⁺ , 0,2 g/1 of Cr³⁺, 0,8 g/1 Fe and 0,5 g/1 Cu. As a result, an efficiency of Cr recovery of over 95 %.

The mud resulted with a umidity of 15 - 20%, with 10-15% ammonia dychromate, is dryed at a temperature of 100 - 111° Celsius time of

5-6 Hours and is then calcinated at 500 - 6oo Celsius obtaining an conglomerate of metalic oxydes of Cr 3+, Fe and Cu.

The ammonia dychromate included in the mud is thermically decomposed by calcination according to the reaction :

(NH^)₂Cr₂0^^" * Cr₂0₃ + H₂® + N₂f (4)

The installation for the retrieving of metals from the used chroming solution is composed from a distributor (2) mobile of gas ammonia, made out of lead and placed at the bottom interior of a lead plated tub. The distributor 2 is connected through a tube 3 flexible with an ammonia container kith a pressure gauge 6, mounted on a push-kart which sustains by a handler 7, an electrochemical sensor 8 for the ammon ia. The variation of PH value is indicated by a PH - meter 9, attached to the chroming tub l.The evacaation of the treated solution is made with a aspiration pump 11, by pipes 10 and 12, towards a Press-filter 13 The filtered material is retained in a reservoir 15 and the mud is put into a container 16 for drying and then calcinated in an oven 17 situated near a mill 18 with balls tø grind the usual metalic oxydes to a granulation of maximum 30 u. The dust of Metalic oxydes may be used as pigment for an alchidic anti -rust grounding.

Example : Into the tub 1 there is a quantity of 1000 1 solution (water chroming used ) with temperature of the environement,with the fallowing composition : 200 g/1 Cr⁶⁺ ,18 g/1 Cr³⁺ ,12 g/1 Fe, 5 g/1 Cu and a ph of 0,5 treated with liquefied ammonia under a pressure of 35 AT from container 4,made with a valve and pressure gauge 6, mounted on a push-kart 5 for transportation. The gas ammonia has been introduced into the solution with the help of the distributor 2, from lead,pis ced at the bottom of the tub l,with a debit of 0,8 l/min and connected t to container 4 by the flexible tube 3, a period of 70 min, to the obtaining of am PH of 5,8 indicated by the PH- meter 9,when the reactioi of neutralization is practically terminated, signalized by the electro- chemcal sensor 8 placed on the surface of the solution and attached to the handle 7 of the push-kart 5. The temperature in now reaching 78° Celsius.

As fallows, the solution treated is vehiculated by the aspiration pump 11 by pipes 10 and 12 by the filter 13. The filtered material is collected into the retainer 15, in quantity of 860 l,had the fallowing composition : 198 g/1 Cr⁶⁺ ,0,2 g/1 Cr³⁺ ,0,8 g/1 Fe, 0,5 g/1 Cu and PH of 5,8. The mud bread , composed of Cr(0H)₃ Fe(0H)₃ Cu(0H)₂ and with

and then dryed in theand container 16 at temperature of 110°Celsius a period of 6 hours and calcinated in the oven 17 at 600 Celsius. The conglomerate of metalic oxydes rezulted has been grinded in the mill 18 with balls untill reached granulation of 30 u and utilized as pigment in a anti- rust pre - painting.

Claims

1. Method of metal retrieving from used chroming solutions,according to the invention,caracterised by the possibility of treatment of water solution containing 150-l-600gr/l Cr⁶⁺ ,15-20 g/1 Cr ⁺ ,15-20 g/1 Fe and other impuryfing metals as Zn,Cu,Cd,Ni,Al - came from the anodic attack of the pieces chromed within the limit of the environment tempera ure,with ammonia gas 30-40 1/m at pressure of minimum 35 At. period of 1 - 1,5 h,when the temperature of the solution reaches 75-80°C,resulting a water solution of Ammonia dychromate and the precipitation of the impure metals as insoluble hydroxydes, non toxic and re-usable,in the same time with the reaction of neutralization when the PH reaches a value of 5,5 - 6, fallowed by an easy precipitation of the used metal at 100 - 115°C then calcination at 500 - 600°C and the final grinding to a granulation of max. 30 u of the resulted metalic oxydes. *

2. The installation used to retrieve metals from the used water chroming solution.

With a mobil distributor (2) of gas ammonia,made out of lead, laced on the bottom - inside of a tub (l) made also from lead, connected through a tube (/) - flexible to a gas container (4) secured by a pressure gauge (6) mounted by a push-kart (&) with a NH₃ sensor on the handle (8) and(7) and the variation of the PH is indicated by a Ph - meter (9). The solution is handled with the help of a aspiration pump (11) by pipes (10 and 12) to a press - filter (13). The filtrated metal is collected in a container (15) and the conglomerate of precipitated is sent to an other container (16) for drying and then to a calcination oven 17 situated next to a ball grinder (18) for the grinding of the resulted metalic oxydes.