CZ33225U1 - Equipment for mine water after-treatment - Google Patents

Description

The present invention relates to a complex system consisting of a purposefully designed and constructed column device on a pallet platform and a newly developed composite based on biochar modified with double layered hydroxides (LDHs) - hereinafter referred to as LDH-biochar. The equipment itself can be used for verification of various types of solid sorbents intended for effective removal of metals and metalloids from point water sources associated with mining activities polluting the environment. The primary use of the equipment in this case is the verification of the effectiveness and the real application of the LDH-biochar composite in the mine water treatment, especially in locations intensively affected by mineral extraction. The technological solution will contribute to the possibility of using contaminated mine water sources as potential sources for utility water. The use of LDH-biochar itself in remediation practice can contribute to reducing long-term contamination of surface streams and related hydrogeological structures in ore mines and to improving the efficiency of remediation methods.

BACKGROUND OF THE INVENTION

In Slovakia, mine sites are currently being remediated at only a few locations. Passive geochemical barriers (using Fe-based materials such as Fe zeolites, FeCL and NaOH, waste Fe materials) or the method of post-treatment with sand filters are the predominant cleaning technology. The situation in the Czech Republic is similar. In most cases, mine water is not treated unless it significantly endangers the water resources or recipients into which water flows - which are then subject to regular monitoring. Otherwise, eg after uranium mining, etc., the technologies are built primarily on the principle of precipitation and subsequent sedimentation. Special mine water treatment plants are being built for this purpose. Sorption processes and bioremediation or very rarely root water treatment plants are also used to a lesser extent. However, these are mostly processes whose purpose is to deprive mine water of selected elements and substances to the extent that they meet the emission limits for a given type of mine water, and which solve all water flowing from eg inheritance galleries, etc. it is not suitable as utility water.

At present, mine waters are not considered as a potential source of service water due to the sufficient supply of drinking water to all populated areas, but due to prolonged droughts in recent years, there is increasing concern about how to replace utility water, now from water supply systems, other water sources (recycled waste water, rainwater, etc.). One of these potential sources may be certain types of mine water, which in many cases, except for higher contents of metals and metalloids, meet the limits for service water. The purification of mine water from excessive quantities of metals and metalloids therefore appears to be essential for obtaining other potential sources of service water.

The essence of the technical solution

The present technical solution relates to the technology based on sorption of selected metals and semi-metals from mine water through developed sorbents LDH-biochar. Double layered Mg-Fe hydroxides with a molar ratio of 4: 1 were synthesized by the undemanding treatment of available Fe-waste materials. During the coprecipitation reaction with MgCL ^x 6H 2 O in an alkaline medium, part of the divalent Mg ²⁺ cations was isomorphically replaced by trivalent Fe ³⁺ cations. Thus, the hydroxide layers acquire a positive charge, which is compensated by the charge of anions located in the interlayer layer together with the crystal water molecules. Results of the method of energy dispersive microanalysis (EDX) for LDH-biochar confirmed in addition to Fe and Mg also the presence of Si, the contents of trace elements such as K, Ca and AI ranged below

% Wt. The technology according to the present technical solution has no ambition to purify large volumes of water; it focuses primarily on the area of treatment and purification of small amounts of mine water for small consumers, with the aim of potential use of treated water as utility water. The whole device as presented, incl. developed sorption fillers LDH-biochar, serve as a robust mine water treatment plant containing a wide range of unwanted metals and semi-metals for the purpose of obtaining service water, producing a maximum of several hundred liters per day. Thanks to the pallet platform, the device is also easily transportable to less accessible places.

The present invention relates to a mobile pallet device based on a two-column system with a filtration and subsequently a sorption column containing LDH-biochar, which functions as an effective sorbent of metals and primarily semi-metals such as As and Sb. The powder composite is synthesized in two steps: production of Mg-Fe LDHs using a solution after acid extraction of Fe sludge and subsequent modification of the wood biochar surface by these LDHs. Detailed methodology of the synthesis of LDH-biochar composite is the subject of the certified methodology No. M049 / M / 2019 (Veselská V., Sillerová, H., Hudcová B., Trakal L., Lacina P. Methodology for the preparation of double layered hydroxides from waste materials and their use in the modification of biochar for the purpose of removing metals and metalloids from mine water. Certified methodology, 2019, 16p.). First, the Fe sludge is decomposed by treatment with sulfuric acid and the obtained Fe leach is used as an input reactant to the synthesis of LDHs. The Fe extract is diluted with water and then the magnesium chloride is dissolved in the hydrated form. Then, a wooden pyrolyzed biochar is added to the solution in a 2: 1 ratio of LDHs: biochar. The pH is adjusted with KOH solution to > 13 and the suspension is stirred for at least 24 hours at room temperature. After filtering and washing with water, the resulting LDH-biochar is obtained, which has proven to be a more effective sorbent of said elements than commercially available carbon-based materials. Therefore, this material has been selected as an effective sorbent in the mine after-treatment process as the final stage of the overall water purification or treatment process.

The present equipment using the LDH-biochar material is designed for efficient mine water treatment, especially in sites intensively affected by mineral extraction. Its use will increase the efficiency of the treatment especially for point sources of contaminated mine water, which could be further used in another way (irrigation, service water, domestic use, in smaller plants, etc.). This minimizes costs while applying the sorbent to a wider range of contaminants.

The apparatus according to the present invention comprises the following parts:

• The aeration tank - preferably a cylindrical polypropylene tank with a volume of approx. 50 liters - serves as an aeration storage tank, to which raw mine water is pumped directly from the source by any external pump. The tank contains an aeration element (eg D-REX®-disc diffuser, OTT group, Germany) connected to an air source, such as an air blower (JDK 40, Secoch, Czech Republic), through which the entire tank volume is continuously aerated to precipitate hydrated iron oxides from mine waters, which could reduce the sorbent capacity of the sorbent in a subsequent sorption step. The aeration element can be implemented in various ways, eg a disc diffuser, a perforated tube or nozzles, and is connected to an air source (blower, compressor). The aeration element may be located all over or above the bottom of the aeration tank or only in certain portions thereof.

• Sand (filtration) column - preferably fiberglass pressure column of cylindrical shape with a total volume of 22 L (eg RT 8x35 HW, Aquaterm, sro, Czech Republic), diameter 20 cm, height 89 cm - which is filled with filter quartz sand (preferably fraction) 0.7 to 1.2 mm). Water with precipitated hydrated Fe oxides from the aeration tank is fed to the column head by means of a pump (for example a 200G booster pump, Aquaterm, s.r.o., CR). The purpose of this step is to separate the precipitated hydrated Fe oxides from the mine water. A barometer (for example PSD-30, WIKA, Germany) can be placed on the inlet to monitor the column for possible fouling. The column head is preferably provided with a three-way valve which is also possible

-2GB 33225 U1 to flush the column in the opposite direction if it is clogged with iron sludge.

• Equalization tank - a second, preferably polypropylene, preferably cylindrical tank having a volume of about 50 liters, which is located between the sand (filtration) and sorption column. This tank is supplied with water from the sand filtration (sand column) and serves as a buffer retention tank before the inlet to the sorbent column.

• Sorption column - preferably a 22 L cylindrical fiberglass pressure column (eg RT 8x35 HW, Aquaterm, sro, Czech Republic), diameter 20 cm, height 89 cm - which is filled with a mixture of filter sand (preferably fractions 0.7 to 1.2 mm) and LDH-biochar in weight ratios from 4: 1 to 20: 1, preferably 15: 1. Here, the inorganic contaminants monitored are absorbed. By means of a pump (for example, booster pump 200G, Aquaterm, s.r.o., CR), water from the buffer tank is passed to the bottom of the sorption column, which passes through the sorption material and exits at the top of the sorption column. A barometer (eg PSD-30, WIKA, Germany) can be placed at the column inlet to check for possible fouling of the column, and a flow meter (eg SM4000 magnetic-inductive flow sensor) that provides information on the amount of water treated.

The aforementioned parts are interconnected by a connecting pipe (s), preferably polypropylene pipes. All components are attached to an aluminum frame and the whole device is placed on a pallet, preferably plastic, which allows easy handling of the whole device even in less accessible areas. The overall dimensions of the device are preferably 120 x 80 x 120 (wxdxh). The device can be easily transported by car, eg pickup, delivery, etc. All electrical appliances (pumps, blower, measuring elements, etc.) are connected to an electric source, for example wall switchboard (230 / 16A) with 230 V power cable also part of the entire device - mounted on an aluminum frame. In the event that the mains power supply is not available, the generator can serve as the source. The whole technological solution of the column system is thus designed to be a completely independent complex, through which it will be possible to verify various types of powder sorption materials even in hard-to-reach places without the possibility of connection to the power network.

The device is therefore able to combine 3 technological stages:

1) Aeration - oxidation of dissolved forms of Fe and precipitation of Fe in the form of hydrated oxides fe ¹¹¹ (rust sludge)

2) Filtration - capture of precipitated hydrated oxides fe ¹¹¹ which absorb a certain amount of metals and semi-metals; it also removes suspended particles and clarifies the water

3) Sorption - trapping of metals and metalloids that were not removed by previous filtration on solid powder sorbents.

In most cases, mine waters contain a high proportion of Fe, which precipitates in the form of hydrated oxides Fe ¹¹¹ (rusty sludge) when water flows to the surface and is aerated. This sludge can clog the sorption column, reduce its efficiency and increase pressure losses. In order to prevent these effects, the aeration and filtration step is included in the overall process. In addition, the trapped hydrated oxides in the sand filter form a filter cake which also assists in the sorption of some metals and metalloids and thus contributes to the overall efficiency of the equipment being operated. If the mine water is clear and does not contain high iron concentrations, only a sorption column can be connected without prior aeration and filtration. In addition, the installation as a whole allows two sorption columns to be connected in series mode for higher efficiency.

Clarification of drawings

Giant. 1. Schematic description of mine after-treatment equipment: 1 - aeration tank, 2 - external pump for water supply to aeration tank, 3 - aeration element, 4 - air blower, 5 - sand (filter) column, 6,11 - pump for water supply to the column, 7.14 - barometer, 8 - three-way valve, 9 - buffer tank, 10 - sorption column, 12 - column bottom where water is supplied, 13 - outlet of sorption column from where water flows, 15 flowmeter, 16 - portable pallet, 17 - power supply.

Giant. 2. Scheme of field experiment, location of car with equipment in field conditions.

Giant. 3. Proportion of captured (light gray area) and non-captured (dark gray area) As and Sb in total input concentration As, Sb for sand filtration (a, d), for LDH-biochar composite column (b, e) and for whole device (c, f).

Giant. 4. Breakdown curves of the field experiment performed for the sorption column (a) and for the whole device (b). The differences between filtered (black symbols) and unfiltered (gray symbols) samples are negligible in the case of a sorption column, confirming the efficiency of the aeration and filtration steps throughout the column equipment for removing contaminants bound to insoluble forms and the subsequent purification capability of the sorption column for insoluble forms. As and Sb in mine waters.

Examples of technical solutions

Preparation of material LDH-biochar

Synthesis of LDH-biochar composite was performed according to the certified methodology No. M049 / M / 2019 (Veselská V., Šillerová, H., Hudcová B., Trakal L., Lacina P. Methodology of preparation for double layered hydroxides from waste materials and their use in biochar modification for the removal of ametaloid metals from mine water. Certified methodology, 2019, 16p.). First, the Fe sludge was decomposed by treatment with 2M H2SO4, in a solid-liquid phase ratio of 1: 5 at 20-25 ° C for 24 hours. The obtained Fe leach was further used as a starting reactant for LDHs synthesis after centrifugation and filtration. According to the synthesis conditions for LDHs having a molar ratio of 4: 1, the Fe extract was diluted in 200 ml of deionized water in a ratio of 100 ml of Fe extract and 100 ml of deionized water. Subsequently, 30.49 g MgCL ^χ 6H 2 O was dissolved in the total volume. For the purpose of synthesizing the LDH-biochar composite, wooden pyrolyzed biochar was added in a fraction <0.5 mm with a surface area of 257 m ² / g in a 2: 1 LDH: biochar ratio. The suspension was stirred vigorously and the pH was adjusted with 2.5M KOH solution up to 13.3. Subsequently, the suspension was stirred for 24 hours at 20-25 ° C. After this time, the suspension was filtered by vacuum filtration and the solid phase was repeatedly washed with demineralized H 2 O to remove residual traces of chemicals such as Cl. The total yield from one synthesis of the LDH-biochar composite was 35 g (23 g LDHs + 12.5 g biochar), corresponding to the desired 2: 1 ratio.

Application of mine water treatment equipment at Pezinok site; Slovak Republic

1. Characteristics of the area

The device with the present composite LDH-biochar was tested on-site in the Pezinok Ore Mine in the southwestern part of Slovakia. It is a locality where antimony ore (Pezinok - Kolársky vrch) was mined in the past. Within the Slovak State Program for the Remediation of Environmental Burdens, this site is included among the sites recommended for monitoring. Mining in the deposit was terminated in the 1990s and has not been given since

No remediation measures have been taken at the site, except for the introduction of the sludge surface by inert construction waste. Due to the oxidative decomposition of sulphide minerals such as arsenopyrite (FeAsS) and antimonite (SbzSs), potentially toxic elements, especially As and Sb. The main sources of contamination are large insufficiently insulated tailings ponds and mine water discharges from galleries. For on-site column testing, contaminated water was selected from a drainage channel draining water from a collecting tank in which water from several galleries and sewage sludge flows down. The mean As concentration at the time of field verification was 1420 pg l ¹ and the average Sb concentration was 410 pg l ¹ . The water temperature at the time of sampling was on average 12 ° C and the pH of the water was 7.5. Based on long-term monitoring of the given area, it can be stated that the selected offtake point represents a representative source of contaminated water and at the same time it is easily accessible from the local road (Fig. 2). The specification of the selected area is the natural co-precipitation of As with Fe and the formation of Fe oxyhydroxides, which are capable of naturally absorbing a certain percentage of As. In order to distinguish this natural attenuation of contaminants and the sorptive capacity of the LDHbiochar for As composite itself, sand filtration was pre-sorbed in the tested system.

2. Field verification of the column system

The sorption column 10 of the system schematically described in FIG. 1 was filled with an LDH-biochar composite which was mixed with sand of a grain size of 0.7 to 1.2 mm to minimize pressure losses with respect to pump performance (see Table 1). The total volume of material in the sorption column 10 was about 20.5 L. An equal volume of pure filter sand of 0.7 to 1.2 mm grain size was used in the pre-sand (filter) column 5. The aeration tank 1 was filled with contaminated water from the drainage channel at regular intervals through the pump 2 during the experiment. From the aeration tank 1, the water was discharged to the head of the sand column 5. The water, after flowing through the filter sand column 5, accumulated in the buffer (retention) tank 9. The mine water purification step itself took place on the sorption column 10 through which water flowed from bottom to top. The flow rate was purposefully controlled and controlled throughout the experiment (Table 1). Samples at the outlet of the sorption column 10 were taken regularly after approximately 100 to 2001 through the system.

In addition to sampling at the outlet of the sorption column 10, water samples were also taken at regular intervals at the plant entrance itself, after aeration from the aeration tank 1, and at the exit of the sand column 5. The total volume of mine water flowing through the system during the experiment was The concentrations of As and Sb in mine water samples were determined by atomic emission spectrometry with optical detection (ICP-OES, Agilent Technologies 730 Series, USA, FZP CULS Prague).

Tab. 1. Field column experiment parameters.

LDH biochar (kg) 2 Sand (kg) 30 Sorbent / sand ratio 1: 15 Flow (1 hour ¹ ) 85-138 ± 2 Sorption bed height (cm) 75 Sorption bed diameter (cm) 19 Dec

3. Results - confirmation of device functionality and sorption ability of the tested composite LDH-biochar

-5 CZ 33225 U1

In order to confirm the complex efficiency of the column system and the ability of the composite to capture target contaminants, the input and output concentrations of As and Sb for sand filtration, for the sorption column with the LDH-biochar composite and also for the whole plant were compared (Fig. 3). The whole device effectively removes As and Sb from mine water, both on sand (approximately 42% As, 9% Sb) and sorption column (approximately 66% As, 19% Sb) (see Fig. 1.). Overall, the device in the described arrangement is more efficient for removing As, which is represented by a significantly larger proportion of light gray area to dark gray in the graphs (Fig. 3c, f). In particular, the sand filtration step (Fig. 3a), where the proportion of As trapped is significantly higher than in the case of Sb (Fig. 3d), contributes to the higher efficiency of As removal. The reason is the already mentioned fact that the precipitated hydrated oxides 1e separated in this step can to some extent naturally bind part of the dissolved As, which has a significantly higher affinity for these oxides than Sb. The LDH-biochar powder composite alone is capable of capturing most of the residual As (Fig. 3b) as well as smaller amounts of Sb (Fig. 3e). In both cases (As and Sb), LDH-biochar plays a dominant role in their removal from mine water. It is also apparent from the results that the column device in this arrangement with the specific parameters given in Tab. 1. would be able to remove As even further from the water, but the additional amount of trapped Sb would be negligible.

The relative amount of As and Sb (%) bound to the undissolved particles at each sampling point, ie at the inlet of the plant, after aeration from the aeration tank 1, at the outlet of the sand column 5 and at the outlet of the entire plant was determined by analysis samples filtered using a 0.45 µm syringe filter to remove suspended particles. The results show that As, unlike Sb, As is already present in the mine water in the form bound to undissolved particles in a relatively significant amount (Table 2). The aeration step increases the increase of the As concentration in these undissolved particles, which again confirms the binding to 1e precipitates due to aeration. Compared to the inlet, the concentrations of both contaminants in undissolved form are considerably lower at the outlet of the apparatus, reflecting the overall efficiency of the apparatus in removing both soluble and insoluble forms of As and Sb.

Tab. 2. The relative amount of As and Sb removed by means of a 0,45 μηι filter at each sampling point within the column apparatus.

As (%) Sb (%) input mine water 28.1 7.93 aeration water 40.5 8.18 water after sand column 2.20 0.50 output mine water 3.47 0.77

The content of As and Sb in the undissolved form after passing through the aeration column (Table 2) corresponds to the values removed by the amounts of As and Sb during sand filtration within the column apparatus (42% As and 9% Sb removed). It can therefore be said that the sand column removes all suspended solids from the water, as in the case of a 0.45 μιη pore size filter. The content of suspended solids in the subsequent steps is negligible, and therefore the sorption column 10 itself is "protected" from clogging by the sand filter, thereby extending its service life.

The ratio of output and input concentrations As and Sb (c Co ¹ ) in dependence on the total volume of mine water flowing through the system during the field experiment is shown by breakdown curves (Fig. 4.). The ratio of c Co ¹ = 0 corresponds to 100% removal of As and Sb, while c Co ¹ = 1 corresponds to 0% removal of As and Sb. The shape of the breakdown curve depends on the water flow through the column, the amount of sorbent, the size of the column, the concentration of As and Sb in the input water. Ideally, the adsorbate concentration at the outlet is zero for as long as possible (c co ¹ = 0), then it reaches the breakdown point (c co ¹ = 0.05) where c

-625 33225 U1 co ¹ increases to saturation point (c Co ¹ = 0.95). The shape of the curve between the breakdown point and the saturation point depends on the adsorption kinetics and adsorption isotherm of the process. The course of the breakdown curve obtained during the field experiment at the Pezinok site was influenced by some changes such as flow settings, variable As and Sb concentrations due to precipitation, interruption of the experiment due to various technological operations (filter column flushing, overnight shutdown, etc.). c co ¹ (Fig. 4., rectangles). The breakdown curves confirmed the higher efficiency of the LDH-biochar composite for the removal of As from mine water - the ccn ratio ranged from 0.2 to 0.5 for most of the experiment. The value increase is gradual and even decreases slightly again at the end of the experiment, which may be related to the decreasing flow rate. The LDH-biochar composite is capable of retaining 50% As of mine water after 5 days of the experiment. The breakdown curve Sb has a similar gradual increase as in the case of As, but the c- ¹ ratio is much higher and ranges from 0.7 to 0.95. At the end of the experiment, only 5% Sb.

5. Evaluation of technical solution

Within the on-site experiment at the Pezinok locality, the complex functionality of the designed and subsequently assembled column equipment was verified directly in the field, and also the efficiency of the developed LDH-biochar material in the removal of metals and metalloids from mine water was verified. Sorption to the composite was determined as a post-purification stage, therefore the sorption itself was preceded by aeration and filtration in order to remove coarse contamination and partly also the contamination monitored. The equipment acted as a complex technology, by which approximately 80% As and 26% Coll. Were removed from the mine water (less than 4000 l). It is clear from the above that the device can also be used to test or utilize a wide range of other solid sorbents, but the work of this study was solely a newly developed LDH-biochar composite. It is therefore a device for specific applications and purification of point sources of mine water for the purpose of obtaining service water, as well as for testing various materials for the purpose of their up-scaling and introduction into remediation practice.

PROTECTION REQUIREMENTS

Claims (9)

Mine treatment plant, characterized in that it comprises a pump (2) for supplying mine water to an aeration tank (1), an aeration tank (1) provided with an aeration element (3), adapted to be connected to an air source (4), wherein the aeration tank (1) is connected via a connecting line and a pump (6) to a sand column (5) which is connected via a connecting line to a buffer tank (9) which is further connected to a sorption tank via a connecting line and a pump (11) column (10). Device according to claim 1, characterized in that the aeration element (3) is selected from the group comprising a disc diffuser, a perforated tube, a nozzle. Device according to claim 1 or 2, characterized in that a barometer (7, 14) is further provided at the inlet of the sand column (5) and / or at the inlet of the sorption column (10). Device according to any one of the preceding claims, characterized in that the head of the sand column (5) is further provided with a three-way valve (8). Device according to any one of the preceding claims, characterized in that a flowmeter (15) is arranged before entering the sorption column (10). Device according to any one of the preceding claims, characterized in that it is provided with an electrical source (17) for connecting the electrically driven parts of the device. -7 GB 33225 U1 Device according to any one of the preceding claims, characterized in that it is arranged on the pallet (16), preferably the pallet (16) is plastic. Device according to any one of the preceding claims, characterized in that the sand column (5) 5 contains quartz sand, preferably having a grain size of 0.7 to 1.2 mm. Apparatus according to any one of the preceding claims, characterized in that the sorption column (10) comprises a mixture of quartz sand, preferably having a grain size of 0.7 to 1.2 mm, and a biochar modified with double-layered Fe, Mg-hydroxides in the sand. a weight ratio of 1 part by weight of biochar to 2 parts of double layered Fe, Mg-hydroxides, the weight ratio of quartz sand to modified biochar being in the range of 4: 1 to 20: 1, preferably the ratio is 15: 1. Device according to any one of the preceding claims, characterized in that the buffer tank (9) and / or the connecting pipe are made of polypropylene.