WO2016001838A1

WO2016001838A1 - Method for treating salty water

Info

Publication number: WO2016001838A1
Application number: PCT/IB2015/054908
Authority: WO
Inventors: Guy Vanderghote; Isabelle Baudin; Maïté BRUGIONI; Jocelyn LEVEQUE
Original assignee: Suez Environnement
Priority date: 2014-06-30
Filing date: 2015-06-30
Publication date: 2016-01-07

Abstract

The invention relates to a method for treating heavy metals in liquid effluents, said method comprising a physicochemical step combined with an ion-exchange step.

Description

PROCESS FOR TREATING EH SALTS WATER

The subject of the present invention is a new process for the treatment of liquid effiuents loaded with metals, in particular salts laden waters.

5 Globally, wastewater treatment is the first public health issue.

Wastewater is all the water charged with various elements coming from the population but also from commercial and industrial activities and which are likely to pollute the environment in which they will be dumped. This is why, in order to respect these different environments, treatments are performed on these effiuents before discharge to the natural environment or in a sanitation network.

Among the elements to be treated, heavy metals are found such as zinc, nickel, chromium, copper, thallium, ^arsenic, lead, s mercury and cadmium which are important contaminants ecosystems and the food web,

Many solutions have been made to treat heavy metals, in the form of different methods, all of which have disadvantages.

- the physico-chemical processes induce, when one wishes to reach high technical performances, significant operating expenses (OPEX) related to the cost of the reagents. Moreover, these processes use sulfur-containing chemicals, for example sodium sulphide (α ₂ S) or tri-mercaptan, which have a negative impact on the environment and do not perform well in case of concentration peaks.

ion exchange processes which use chelating resins allowing the selective fixing of heavy metals also induce significant operating expenses (OPEX) related to the cost of regeneration of the resins or that of their renewal, this cost being well known high in the case of treatment effiuents loaded with metals. In addition it is it is essential to manage used resins which are considered as solid hazardous waste and to manage the eluates which are considered as dangerous liquids,

membrane techniques that use ultra-thinning, nanofitration or reverse osmosis membranes that lead to significant operating expenses (OPEX) because the conversion rate is often less than 50% for effluents loaded with salts ( management and elimination of concentrates). Moreover, these techniques are unusable because of the rapid and irreversible clogging, when the waters are heavily loaded with salts, especially calcium and sulfate, and

- the techniques of evapo-concentration or o-o-crystallization induce significant operating expenses (OPEX) due to the energy needed for evaporation and high capital expenditure (CAPEX). In addition, there is a need to manage brines either by eliminating them or by enhancing them,

Also, there is a need to have a technique that both optimizes OPEX, in particular by reducing the quantities of reagents used and technical performance, in particular: limitation / suppression of releases of hazardous substances (mercury , cadmium, lead, zinc, etc.), better purification efficiency, lower or even zero metal emission levels, control of emission peaks without overdosing of chemicals.

However, the inventors realized that by coupling two methods, a physico-chemical method and an ion exchange method, it was possible to provide a metal treatment process on effluents loaded with salts which solves the problem. all the problems mentioned above.

Thus, the subject of the present invention is a process for treating Dung metals present in liquid effluents, loaded with salts, in particular salts-laden waters, said process comprising the following steps:

at. treatment of the effluent liquid may contain heavy metals selected from a group ie neutralizing agent comprising sodium hydroxide in particular, ie _f milk of lime milk of magnesia, to a pH of 5 to 6,

b. coagulation of the treated tributary to a), during which a dose of coagulant is injected into said effiuent,

vs. precipitation of the mixture obtained in step b) with a neutralizing agent chosen from the group comprising especially sodium hydroxide, lime milk, milk of magnesia, at a pH of 9 to 10,

d. flocculation of the mixture obtained during coagulation step b) or the mixture obtained during the treatment step with a neutralizing agent c), during which an injection of fioculant into said mixture is carried out in order to agglomerate the particles in suspension under form of fiocs,

e. elimination of the chips formed in step d) and recovery of the liquid,

f. treatment of residual suspensions in step e) by fiitration,

boy Wut. contacting the recovered liquid in step f) with an ion exchange resin capable of adsorbing one or more heavy metals or placed in successive contact with several resins ^ion exchange, each resin being adapted to adsorb one or more metals in order to reduce the concentration of heavy metals present in said liquid,

h. recovery of the heavy metal free liquid,

Heavy metal-free means a liquid whose concentration of heavy metals is in accordance with the emission values in the natural environment, ie less than 0.01 mg / L

According to the invention, step a) can be carried out according to any technique known to those skilled in the art, in particular by mixing the slaked lime in the form of milk of lime with the effluent to be treated. The pH is adjusted by any known acid, especially 33% hydrochloric acid in a range of 5.5 to 8.5. According to the invention, the coagulation step b) can be carried out by addition of a coagulant. This step can be carried out separately from step a) or simultaneously with step a). In both embodiments, the coagulated mixture is subjected to a flocculation step d).

The precipitation step c) is optional, that is to say that step d) can be done directly after step b).

At the end of step d), the fioc is removed, for example by decantation (step e), according to techniques known to those skilled in the art and the decanted liquid is filtered, for example on a sand filter (step f). ) before being contacted with ion exchange resins (step g).

The coagulation and flocculation steps are carried out by techniques known to those skilled in the art such as those described in the Water Technical Memo Tenth Edition Volume 1 Chapter 3 page 185 and following Editor Degrémont Suez), Coagulation consists of addition of a coagulant such as, for example, trivalent cations, in particular iron or aluminum salts, allowing the destabilization of the colloidal particles present in the water and the neutralization of all the electronegative charges of these particles. During this step, the neutralized particles begin to agglomerate by mechanical agitation to form micro-flocs. These micro-flocs are too small to be eliminated, especially by decantation. Also the flocculation step is necessary to fatten these flocs.

According to the invention, the liquid decanted (step e) and filtered (step f) can be brought into contact with a single resin capable of capturing several heavy metals or on a battery of resins each being capable of fixing one or more heavy metals By way of example of a resin, mention may be made of Ianxess monoplus TP207, Amberlite IRC 748, and Anmonus TP 214, Ambersep GT 74.

At the end of step g), the heavy metal-free liquid is recovered and can be discharged into the natural environment or into a sewerage system.

The process according to the invention, by virtue of the physicochemical treatment, also makes it possible to reduce its fluorine concentrations up to meeting the emission limit values in the natural environment, the emission limit value in the natural environment! in France is 15 mg / ί or less than the detection limit.

According to the invention, the process allows the treatment of heavy metals such as zinc, nickel, chromium, copper, thaiium, arsenic, lead, mercury and cadmium which are present in the metal. water by precipitation (by the neutralization or insoluble agent) and adsorption on resin. According to the invention, it is possible to eliminate one or more of these metals depending on the type of resin used. The person skilled in the art, in the light of this general knowledge, will be able to choose and combine the appropriate type of resin.

The process according to the invention is applicable to any liquid medium, in particular any aqueous effluent, in particular the smoke flushing effluents from incineration plant of non-hazardous waste or hazardous waste, the leachates from the plant. storage of non - hazardous waste, effluent from surface treatment, mining efficiency, coal or gas power plants.

The treatment method according to the invention makes it possible to obtain, at the end of the process, a concentration of each of the heavy metals of less than 0.01 mg / l.

According to the invention, the method may further comprise, after step g), at least one step of emitting the resins to desorb the heavy metals attached to said resins, the recovery of the eluates containing said heavy metals and at least one regeneration step of said resins for subsequent use in a new cycle. The resins used for adsorbing mercury are not regenerable because of the complexity of the regeneration method. These resins, such as used resins (resin having reduced efficiency after several production / regeneration cycles) are eliminated in a conventional manner. .

The regeneration eluates of the resins comprising high concentrations of heavy metals can be subjected to physicochemical treatment (recycling upstream of the process). Indeed, the resins are a refining treatment (secondary treatment) and the physicochemical is a primary treatment suitable for the treatment of effluents concentrated in metals. According to the invention, the emission levels can be controlled by a tool for online and continuous monitoring of the metal content at the inlet and the outlet of the ion exchange resin treatment; according to the flight of metal, it is possibie to know precisely ^the state of saturation of the resin and if necessary to trigger the regeneration of resins.

Still according to the invention, the operation can be optimized by setting up a control of the process in order to guarantee the emission levels (quality of the treated water) while optimizing / limiting the regenerations of the resins (and therefore the OPEX of this post):

recovery and processing of the data from the analyzers and predictive calculation of the cycles remaining to satisfy the desired water quality.

display of the real-time count of the remaining cycle in order to regenerate only when the metal leaks on the resins do not satisfy the desired water quality.

In order to better understand the method that is the subject of the present invention, an implementation mode is described below. It remains of course that this is only an example having no limiting character. In this description, reference is made to Figure 1 of the accompanying drawings which is a diagram illustrating the various steps of the method according to the invention.

In this figure, the effluent to be treated is directed to a tank (1) provided with a stirrer in which lime and coagulant are also added while controlling the pH; The effiuent thus treated is brought into a tank (2) and again treated with lime, under controlled pH, then the mixture is brought from the tank (2) into a tank (3) in which a Hocuiant is added after flocculation. the flocculated mixture is fed from the tank (3) into a lamellar settling tank (4) and the floc is removed. The liquid decanted and filtered on a sand filter (RI) is then subjected to a passage over different resins (R2 = resin 1 and R3 - resin 2), each of these resins being able to adsorb one or more heavy metals than the it is desired to remove the effluent to be treated. After passing on these resins, the liquid free of heavy meta ux is rejected in the natural environment or in a sanitation network.

The performances of the process according to the invention compared to those of the known processes of the prior art are gathered in Table 1 below.

Table 1

The process according to the invention has the following advantages:

- an OPEX gain of 25 to 30% compared to the physico-chemical sector only, an environmental gain due to the reduction or elimination of the sulfur products conventionally used for the precipitation of metals and

a technical gain linked to the better metal reduction,

Claims

Process for the treatment of heavy metals present in liquid effluents charged with metals, in particular salts-laden waters, said process comprising the following steps:

at. treatment of the liquid effluent likely to contain heavy metals with a neutralizing agent selected from the group consisting in particular of sodium hydroxide, lime milk, milk of magnesia, at a pH of 5 to 6,

b. coagulation of the effluent treated in step a),

vs. precipitation of the mixture obtained at recap, b) with a neutralizing agent selected from the group comprising in particular its sodium hydroxide, milk of lime, milk of magnesia, at a pH of 9 to 10, d. flocculation of the mixture obtained during the coagulation step b) or the mixture obtained during the treatment step with a neutralizing agent c),

e. elimination of the flocs formed in step d) and recovery of the liquid,

f. treatment of residual suspensions in step e) by fiitration,

boy Wut. in contact with the liquid recovered in step f) with an ion exchange resin capable of adsorbing one or more heavy metals or put in successive contact with several ion exchange resins, each resin being capable of adsorbing one or more heavy metals in order to reduce the concentration of heavy metals present in said liquid,

h. recovery of the heavy metal free liquid.

Process according to Claim 1, characterized in that the heavy metals are chosen from the group comprising zinc, nickel, chromium, copper, thailium, arsenic, lead, mercury and cadmium.

3. Treatment process according to any one of the preceding claims, characterized in that the concentration of each of the heavy metals at the end of the process is less than 0.01 mg / L 4 <Treatment method according to the claim ication I characterized in that it further comprises after step g), at least one step of el ution of the resins to recover said adsorbed heavy metals and at least one step of regeneration of said resins. 5. Treatment process according to claim 1 characterized in that the continuous and continuous monitoring of its metal leakage on the ion exchange resin stage makes it possible to know the state of saturation of the resin and to trigger if necessary 6. The treatment method as claimed in claim 5, characterized in that the leakage of metals on the ion exchange resin stage is the subject of a predictive calculation making it possible to know the duration of the cycle remaining before new regeneration.