Process for treating acidic waters laden with metals and metalloids by passing through a wollastonite medium

Abstract

------ Process for treating acidic waters loaded with metals and metalloids by passing through a wollastonite medium The present invention relates to a process for treating acidic waters having pH values ​​of 1 - 5, in particular 2 - 4 and loaded with metals and metalloids in order to increase the pH and remove the metals and metalloids, characterized in that the flow of water to be treated is passed, in open circulation, through a porous permeable medium formed of wollastonite grains having a D50 of 10 µm - 5 cm, and that the purified waters are recovered having a pH of 6 to 10.

Description

Title of the invention: Method for treating acidic waters laden with metals and metalloids by passing through a wollastonite medium

[0001] The present invention relates to a method for treating acidic waters loaded with metals and metalloids by passing through a wollastonite medium.

[0002] Wastewater from industrial processes and mining effluents is a major environmental problem worldwide. This wastewater has an acidic pH and a very high concentration of metals and / or metalloids, such as cadmium, copper, zinc, or arsenic. To prevent this wastewater from causing harmful pollution to the environment, it is necessary to treat it to increase its pH and remove the metallic and metalloid elements.

[0003] Neutralization treatments using reagents exist, but these prove expensive for large volumes. Various filters, drains, or barriers also exist, but their effectiveness is limited over time and they generate large quantities of waste to be managed.

[0004] Fernandez et al. described the use of wollastonite for the treatment of mine water for the removal of arsenic and metals.

[0005] Wollastonite is first ground to a size of 5 mm, and the pure wollastonite crystals are then hand-sorted. These crystals are then ground into a powder with grains smaller than 63 µm. This powder is then placed in a polyethylene centrifuge tube with mine effluent water. The tube containing the sample and the mine effluent is then agitated using an orbital shaker for a period ranging from 15 to 80 days.

[0006] This process only allows a small increase in pH from 2.1 to 3.5 and does not allow good efficiency on zinc.

[0007] The present invention therefore aims to resolve these drawbacks in order to achieve neutralization of industrial acid waters or mining effluents to be treated and a reduction of the concentrations of metals in solution.

[0008] To this end, the present invention relates to a process for treating acidic waters having pH values ​​of 1-5, in particular 2-4 and loaded with metals and metalloids in order to increase the pH and remove the metals and metalloids, characterized in that the flow of water to be treated is passed, in open circulation, through a porous permeable medium formed of wollastonite grains having a D50 of 10 pm-5 cm, preferably of 71 pm, and that the purified waters are recovered having a pH of 6 to 10.

[0009] The diameter D50 gives the median diameter of the grains, half of the grains have a higher diameter and the other half a lower diameter.

[0010] Open circulation means that the flow of water to be treated is constantly renewed in the permeable porous medium formed by the wollastonite grains.

[0011] The waters to be treated may be loaded with at least one of the following elements: Al, Fe, Ni, Zn, Cd, Pb, Mn, Co, Cu, As, Cr, V, U, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu.

[0012] Wollastonite can be ground and sieved to a grain size of 10 µm - 5 cm, preferably 100 µm.

[0013] In one embodiment, the wollastonite medium can be placed in a column in which the flow of the water to be treated is upward or downward.

[0014] In another embodiment, the wollastonite medium can be arranged along a bed through which the flow of water to be treated passes from one edge to the other.

[0015] The wollastonite medium can exhibit a porosity of 25-50%, for example 40%.

[0016] In the case where the wollastonite medium is placed in a column, the porosity can be calculated from the density of the wollastonite and the mass of wollastonite introduced into the column, thus determining the volume of wollastonite in the column. The porosity is obtained using the following formula:

[0017] Porosity = (Total volume of column - volume of wollastonite) / total volume of column.

[0018] For the calculation of the porosity in a bed, the porosity can be calculated in the same way as for a column from a chosen volume within the bed and the mass of wollastonite within this bed.

[0019] The final ratio of treated water to wollastonite can be 2 - 250 L / kg of wollastonite.

[0020] The water to be treated can be passed through with a flow rate of 0.1 - 10 L / kg of wollastonite / h.

[0021] After treatment of 0.1 - 40 days, a wollastonite loaded with metals and metalloids can be recovered.

[0022] The water treatment time depends mainly on the initial load of metals and / or metalloids to be removed from said water.

[0023] If the first objective is to reduce the metallic load in the waters before integration into a new process or release into the natural environment, the metals thus fixed on the recovered wollastonite can be used as a resource, particularly with regard to a number of rare metals, and can therefore be used in recovery processes.

[0024] Before the introduction of the water stream to be treated through the permeable porous medium formed of wollastonite grains, said stream may have been pre-treated by a coagulation-flocculation type device.

[0025] The following examples illustrate the present invention without however limiting its scope.

[0026] Example 1: Treatment column for water from industrial processes and mining effluents

[0027] Fig. 1 presents a schematic view of a column used in the process according to the invention.

[0028] The column is 4 cm long and 1.5 cm in diameter. The column is packed with crushed wollastonite that has been sieved using a 100 µm sieve and has a D50 diameter of 71 µm and a porosity of 0.40.

[0029] Fig. 2 shows the distribution curve of the diameters of wollastonite particles.

[0030] Table 1 below gives the mass composition of the components present in the wollastonite used to fill the column.

[0031] [Tables 1] Component A12O3 CaO Fe2O3 k2o MgO MnO Na2O p2o5 SiO2 so3 C mass % 2.4 37.1 0.04 <l.q. 0,60 0,07 <l.q. 0,01 71,0 <l.q. 0,2

[0032] <l.q. signifie que la quantité du composant en question est inférieure à la limite de quantification.

[0033] Table 2 indicates the predominance of certain elements present in wollastonite

[0034] [Tables2] Elements Cr Cl Co Ni Cu Zn As Cd Sr Ba Pb Proportion (mg / kg) <l.q. 174,1 <l.q. <l.q. <l.q. 44,8 <l.q. <l.q. 43,7 51,4 3,6

[0035] <l.q. signifie que la quantité de l’élément en question est inférieure à la limite de quantification. Example 2#: Water to be treated

[0036] The water to be treated is water from a mine drainage and which has a pH of 3.0, an oxidation-reduction potential of 436.0 mV, a conductivity of 96.0 pS / cm and a total organic carbon of 0.8 ppm.

[0037] Table 3 indicates the quantities of elements present in the water to be treated.

[0038] [Tables3] Elements Ca Mg Na K Si Cl no3 nh4+ SO42 Al Fe mg / L 27.0 28.5 7.8 6.1 15.7 9.56 2.19 0.02 332 9.62 9.24 Elements Mn Cr Co Ni Cu Zn As Pb Cd Ba Sr mg / L 4.74 0.60 485 225 329 755 9.7 0.19 3.87 11.2 156 Example 3#: Water treatment to be treated

[0039] The water from Example 2 is passed through the column of Example 1 in an upward stream at a flow rate of 10 mL / hour for a period of 24 hours.

[0040] Table 4 shows the quantities of metals and metalloids in the solution after 24 hours.

[0041] [Tables4] Elements Al Cr Mn Fe Co Ni Cu Fg / 1 <LQ <LQ 0,1 <LQ 0,02 0,32 <LQ Eléments Zn As Se Sr Cd Ba Pb Fg / 1 <LQ 0,5 <LQ 172,42 <LQ 19,83 <LQ

[0042] <LQ signifie que la concentration de l’élément en question est inférieure à la limite de quantification

[0043] Fig. 3 is a graph showing the evolution of the pH and the redox potential of the solution at the outlet of the column.

[0044] Figures 4 to 6 show the evolution over time of the ratio of input concentrations to output concentrations for certain elements.

[0045] As can be seen in [Fig.3], the rise in pH of the outlet solution is very rapid and reaches a value greater than 9. This therefore makes it possible to provide water with a neutralized pH value.

[0046] In [Fig. 4], it can be seen that the outlet concentrations of the metals are much lower than the inlet concentrations. In particular, the concentration values ​​of lead, aluminum, copper, chromium, iron, zinc, and cadmium fall below the qualification limits no later than 10 hours after treatment.

[0047] Figures 5 and 6 show that certain elements of wollastonite are dissolved and pass into solution; this is the case for chloride, calcium, and potassium ions. These figures also show that ammonium ions are completely retained by wollastonite.

[0048] As can be seen in Table 4, if strontium and barium are not retained by wollastonite, the amounts of aluminium, chromium, manganese, iron, cobalt, nickel, copper, arsenic, selenium, cadmium and lead are considerably reduced after 24 hours compared to the initial amounts.

[0049] The open circulation treatment therefore makes it possible to neutralize the pH of the solution and to trap the metals and metalloids in the wollastonite which can subsequently be recovered for valorization.

Claims

Demands

1. - A process for treating acidic waters having pH values ​​of 1 to 5, in particular 2 to 4, and loaded with metals and metalloids, in order to increase the pH and remove the metals and metalloids, characterized in that the flow of water to be treated is passed, in open circulation, through a permeable porous medium formed of wollastonite grains having a D50 of 10 pm to 5 cm, the wollastonite medium having a porosity of 25 to 50%, the flow of water to be treated being continuously renewed in said permeable medium, the water to be treated passing through the wollastonite medium with a flow rate of 0.1 to 10 L / kg of wollastonite / h and the purified water is recovered having a pH of 6 to 10, D50 being the median diameter of the grains, of which half of the grains have a larger diameter and the other half, a smaller diameter.

2. - A process according to claim 1, characterized in that the waters to be treated are loaded with at least one of the following elements: Al, Fe, Ni, Zn, Cd, Pb, Mn, Co, Cu, As, Cr, V, U, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu.

3. - A process according to any one of claims 1 and 2, characterized in that the wollastonite has been ground and sieved to a grain size of 10 µm to 5 cm.

4. - A method according to any one of claims 1 to 3, characterized in that the wollastonite medium is placed in a column in which the flow of the water to be treated is upward or downward.

5. - A method according to any one of claims 1 to 3, characterized in that the wollastonite medium is arranged in a bed through which the flow of water to be treated passes from one edge to the other.

6. - A process according to any one of claims 1 to 5, characterized in that the final ratio of treated water to wollastonite is 2 to 250 L / kg of wollastonite.

7. - A process according to any one of claims 1 to 6, characterized in that after treatment of 2 hours 24 minutes to 40 days, a wollastonite loaded with metals and metalloids is recovered.

8. - A method according to any one of claims 1 to 7, characterized in that before the introduction of the water stream to be treated through the permeable porous medium formed of wollastonite grains, said stream has been pretreated by a coagulation-flocculation type device.

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