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: Process for treating acidic waters loaded with metals and metalloids by passing through a wol-lastonite medium

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

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

[0003] There are neutralization treatments by adding reagents but these prove expensive for the large volumes to be treated. There are also various filters, drains or barriers but their effectiveness is limited in time and they result in 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 crushed to a size of 5 mm, then pure wollastonite crystals are sorted by hand. These crystals are then crushed into a powder of grains less than 63 pm. This powder is then placed in a polyethylene centrifuge tube with mining effluent water. The tube containing the sample and the mining effluent is then agitated using an orbital shaker for a period ranging from 15 days to 80 days.

[0006] This process only allows a slight increase in pH from 2.1 to 3.5 and does not allow good effectiveness on zinc to be obtained.

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

[0008] To this end, the present invention relates to a method for treating acidic waters having pH values ​​of 1 - 5, in particular 2 - 4 and loaded with metals and metalloids 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 - 5 cm, preferably 71 pm, and that the purified waters having a pH of 6 to 10 are recovered.

[0009] The diameter D50 gives the median diameter of the grains, half of the grains have a larger diameter and the other half a smaller 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 water to be treated can 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 crushed and sieved to a grain size of 10 µm - 5 cm, preferably 100 µm.

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

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

[0015] The wollastonite medium may have 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, which makes it possible to reach the volume of wollastonite in the column. The porosity is obtained by the following formula:

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

[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 for 0.1 - 40 days, 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 in the water to be removed from said water.

[0023] If the first objective aims at reducing the metal load in the water 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, in particular concerning a certain number of rare metals, and can therefore be used in recovery processes.

[0024] Before introducing the flow of water to be treated through the permeable porous medium formed from wollastonite grains, said flow may have been pretreated 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.l] shows a schematic view of a column used in the process according to the invention.

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

[0029] [Fig.2] shows the particle diameter distribution curve of wollastonite.

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

[0031] [Tables 1] Component A12O 3 CaO Fe2O 3 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 preponderance of certain elements present in wollastonite

[0034] [Tables2] Elements Cr Cl Co Ni Cu Zn As Cd Sr Ba Pb Proport-ti on (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 system 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 / 1 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 / 1 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 of Example 2 is passed through the column of Example 1 in an upward flow at a flow rate of 10 mL / hour for a period of 24 hours.

[0040] Table 4 shows the amounts 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 oxidation-reduction potential of the solution at the outlet of the column.

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

[0045] As can be seen in [Fig.3], the rise in the pH of the solution at the outlet 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 metals are much lower than those at the inlet. In particular, the values ​​of the concentrations of lead, aluminum, copper, chromium, iron, zinc and cadmium fall below the qualification limits at the latest after 10 hours of treatment.

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

[0048] As can be seen from Table 4, if strontium and barium are not retained by wollastonite, the amounts of aluminum, chromium, manganese, iron, cobalt, nickel, copper, arsenic, selenium, cadmium and lead are significantly 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 use.

Claims

Claims

1. - Process for treating acidic waters having pH values ​​of 1 to 5, in particular of 2 to 4, and loaded with metals and metalloids 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, and that the purified waters having a pH of 6 to 10 are recovered.

2. - Method according to claim 1, characterized in that the water to be treated is 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. - Method according to one of claims 1 and 2, characterized in that the wollastonite has been crushed and sieved to a grain size of 10 μm to 5 cm.

4. - Method according to one of claims 1 to 3, characterized in that the wollastonite medium is placed in a column in which the flow of water to be treated is ascending or descending.

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

6. - Method according to one of claims 4 and 5, characterized in that the wollastonite medium has a porosity of 25 to 50%.

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

8. - Method according to one of claims 1 to 7, characterized in that the water to be treated is passed through with a flow rate of 0.1 to 10 L / kg of wol-lastonite / h.

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

10. - Method according to one of claims 1 to 9, characterized in that before the introduction of the flow of water to be treated through the permeable porous medium formed of wollastonite grains, said flow has been pretreated by a coagulation-flocculation type device.

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