Method for treating acidic water loaded with metals and metalloids by passing through a wollastonite medium

Abstract

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

Description

Process for treating acidic waters loaded with metals and metalloids by passing them through a wollastonite 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 issue worldwide. This water has an acidic pH and a very high concentration of metals and / or metalloids, such as cadmium, copper, zinc, or arsenic. To prevent this water from causing harmful pollution to the environment, it is necessary to treat it to increase its pH and remove metallic and metalloid elements.

[0003] There are neutralization treatments by adding reagents, but these are expensive for large volumes to be treated. There are also various filters, drains, or barriers, but their effectiveness is limited over 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 hand-sorted. These crystals are then ground into a powder with grains less than 63 µm. This powder is then placed in a polyethylene centrifuge tube with mining effluent water. The tube containing the sample and mining effluent is then shaken 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.

[0007] US patent application US 2009 / 0045136 A1 describes closed-circuit laboratory tests for the absorption of metals from a solution using wollastonite as an absorption material. However, when the tests are carried out in an open circuit, a malfunction occurs.

[0008] Seeking to solve this problem, the present inventors discovered a non-obvious combination of parameters allowing successful filtration in an open environment over a long period of time, these parameters being the flow rate of the water to be treated, the porosity of the wollastonite and the D50 of its grains.

[0009] 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.

[0010] 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 µm – 5 cm, preferably 71 µm, the wollastonite medium having a porosity of 25 to 50%, the flow of water to be treated being constantly 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 that the purified waters having a pH of 6 to 10 are recovered, D50 being the median diameter of the grains, at which half of the grains have a diameter upper and the other half, a lower diameter.

[0011] 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.

[0012] Open circulation means that the flow of water to be treated is constantly renewed in the permeable porous medium formed by the wollastonite grains.

[0013] 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.

[0014] Wollastonite can be crushed and sieved to a grain size of 10 µm – 5 cm, preferably 100 µm.

[0015] In one embodiment, the wollastonite medium may be placed in a column in which the flow of water to be treated is upward or downward.

[0016] 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.

[0017] In the case where the wollastonite medium is placed in a column, the porosity can be calculated from the density of wollastonite and the mass of wollastonite introduced into the column, which allows the volume of wollastonite in the column to be reached. The porosity is obtained by the following formula:

[0018] Porosity = (Total column volume – wollastonite volume) / total column volume.

[0019] For the calculation of 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.

[0020] The final ratio of treated water to wollastonite can be 2 - 250 L / kg of wollastonite.

[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 to be removed from the water.

[0023] If the first objective is to reduce 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, particularly 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 of wollastonite grains, said flow 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] 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 sieved through a 100 µm sieve and having a D50 diameter of 71 µm and a porosity of 0.40.

[0029] Lamontre shows the distribution curve of wollastonite particle diameters.

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

[0031] ComponentAl2O3CaOFe2O3K2OMgOMnONa2OP2O5SiO2SO3C% by mass2,437,10,04 <l.q.0,600,07<l.q.0,0171,0<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 shows the preponderance of certain elements present in wollastonite

[0034] ElementsCrClCoNiCuZnAsCdSrBaPbProportion (mg / kg) <l.q.174,1<l.q.<l.q.<l.q.44,8<l.q.<l.q.43,751,43,6

[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 has a pH of 3.0, an oxidation-reduction potential of 436.0 mV, a conductivity of 96.0 µS / cm and a total organic carbon of 0.8 ppm.

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

[0038] ElementsCaMgNaKSiCl - NO3 - NH4 + SO4 2-AlFemg / l27,028,57,86,115,79,562,190,023329,629,24ElementsMnCrCoNiCuZnAsPbCdBaSrmg / l4,740,604852253297559,70,193,8711,2156 Example 3: water treatment to be treated

[0039] The water from Example 2 is passed through the column of Example 1 in an upward flow at a 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] ElementsAlCrMnFeCoNiCuµg / l <LQ<LQ0,1<LQ0,020,32<LQElémentsZnAsSeSrCdBaPbµg / l<LQ0,5<LQ172,42<LQ19,83<LQ

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

[0043] This 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 to outlet concentrations for certain elements.

[0045] As can be seen in the figure, the pH of the solution at the outlet rises very quickly and reaches a value above 9. This therefore makes it possible to provide water with a neutralized pH value.

[0046] In the figure, we can see that the output 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, nickel cobalt, copper, arsenic, selenium, cadmium and lead are considerably reduced after 24 hours compared to the initial amounts.

[0049] 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 recycling.

Claims

– 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 µm to 5 cm, the wollastonite medium having a porosity of 25 to 50%, the flow of water to be treated being constantly 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 that the purified waters having a pH of 6 to 10 are recovered, D50 being the median diameter of the grains, at which half of the grains have a larger diameter and the other half a smaller diameter. – 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. – 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. – 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. – 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. – Method according to 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. – Method according to 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. – Method according to one of claims 1 to 7, 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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