RU2055818C1 - Method to render harmless electroplating works sewage sediments - Google Patents

Abstract

FIELD: industrial sewage sediments neutralization. SUBSTANCE: suspension of individual hydroxide of heavy or non-ferrous metal or mixture of hydroxides, that is produced during sewage treatment with reactant, is being filtered vertically located porous metal partition of 1,5 mm thick with pores sizes of 3 - 15 mcm under pressure of 0.1 - 0.3 MPa. Regeneration of filtering partition is exercised by air blowing through layer of sediment on partition under pressure of 0.1 - 0.2 MPa within at least 10 minutes. Method allows to decrease concentration of heavy and non-ferrous metals (iron, chrome, nickel, copper, zinc, cadmium, lead, aluminum) in filtrate to 0.1 - 0.3 mg/l and not to use water for regeneration of filtering partition. EFFECT: decreases concentration of heavy and non-ferrous metals in filtrate. 1 dwg, 1 tbl

Description

 The invention relates to the dewatering of hard-to-filter suspensions, in particular hydroxides and hydroxycarbonates of heavy and non-ferrous metals, and can be used to treat sewage sludge generated in engineering, chemical and other industries.

 The most common methods for dehydrating thickened suspensions of hydroxides of heavy and non-ferrous metals formed during the neutralization of washing water of galvanic, pickling and passivation lines are various filtering options with a spin under the action of a diaphragm or centrifugal forces and purging the precipitate with air.

As a prototype of the selected method of dehydration of the thickened suspension of hydroxides of heavy and non-ferrous metals, including the following operations:
filtering the suspension through cotton belting under a pressure of 0.6 MPa for 30 min;
extraction of sediment through the diaphragm under a pressure of 0.9 MPa for 20 minutes;
drying the precipitate with air at a pressure of 0.7 MPa for 20 minutes;
removal of sediment from tissue by gravity;
tissue regeneration by washing with water.

The sludge dehydrated according to the prototype has a thickness of 3 mm, humidity 67%
The prototype method has a number of disadvantages. Firstly, the filtrate obtained by dehydration is a fine suspension containing up to 200 mg / l of hydroxides of heavy and non-ferrous metals, which makes it impossible to reuse it in the process, and even more so dump it into the sewer without additional purification. Cleaning the filtrate obtained by dewatering the sludge under the conditions of the prototype, from metals to the level of maximum permissible concentrations, is a difficult technical task. Secondly, during the regeneration of filter cloth by washing with water, a suspension of metal hydroxides is also formed, requiring additional purification. Secondly, the implementation of the prototype method requires high pressure filtering the suspension (0.6 MPa), pressing the precipitate (0.9 MPa) and drying the precipitate (0.7 MPa). The filter presses of the FPAKM and FPAV type used for the implementation of the prototype are notable for their complexity of construction and high cost, they require highly qualified service.

 The objective of the invention is to reduce the content of heavy and non-ferrous metals (iron, chromium, nickel, copper, zinc, cadmium, lead, aluminum) in the filtrate to 0.1-0.3 mg / l and the exclusion of water consumption for the regeneration of the filtering partition.

 This is achieved by the fact that a suspension of an individual heavy or non-ferrous metal hydroxide or a mixture of hydroxides obtained by reagent wastewater treatment is filtered through a vertically arranged porous metal partition with a thickness of up to 1.5 mm with pore sizes of 3-5 10-15 microns under a pressure of 0, 1-0.3 MPa, and the regeneration of the filter septum is carried out by blowing air through a layer of sediment on the septum under a pressure of 0.1-0.2 MPa with a purge time of at least 10 minutes

 As the filter baffle in the proposed method, a sheet of porous titanium (TU 14-1-1895-76) or porous steel grade X18H15 (TU 14-1-2173-72) with a thickness of 0.2-1.5 mm with a pore size of 3- 5 10-15 μm and a porosity of 20-45%. The proposed method is implemented on a bench installation, a diagram of which is shown in the drawing. The washing water of the passivation bath of zinc coatings after treatment with iron (II) sulfate and neutralization with sodium hydroxide to a pH of 7.5-8.0 was concentrated by settling in a container (1) for 2 hours, after which a thickened suspension of iron, chromium and zinc hydroxides ( composition, wt% iron (III) hydroxide 70, chromium (III) hydroxide 23, zinc hydroxide 7) was poured into a container (2). From the container (2), the condensed suspension under the action of compressed air entered the filter element (3) with a septum (4) made of porous metal fixed in it. In the process of filtering the suspension, a compacted precipitate (5) of hydroxides was formed on the surface of the filtering septum, and the filtrate was sent to a container (6). Upon reaching a certain thickness of the sediment layer on the partition (4), the filtration was stopped and the suspension from the filter element (3) was poured into a container (2); while the compacted layer of hydroxide precipitate remained on the surface of the septum. Then, compressed air was purged through the sediment layer (5); in this case, retained water was displaced from the sediment, and the precipitate dried to a moisture content of 70-75% cracked and without any additional impact fell to the bottom of the filter element under its own weight (3). After unloading the dehydrated sludge from the filter element, the dewatering cycle was repeated as described above. The analysis of the filtrate for the content of iron, chromium and zinc was carried out using an atomic absorption spectrometer AAS-IN.

 Specific examples of the implementation of the proposed method for dewatering sewage sludge from galvanic plants are given in the table. From the above examples it is seen that the proposed method provides the purification of the filtrate to a value of 0.1-0.3 mg / l, which allows you to remove the filtrate from the process without harming the environment (examples 1-3). When the thickness of the filter baffle is more than 1.5 mm (Example 5) and also with the pore size of the filter baffle less than 3-5 microns (Example 8), the pore baffle is clogged by particles of hydroxides, the filtering rate decreases and the partition regeneration process is disturbed. If the pore size of the septum is more than 10-15 μm, the degree of contamination of the filtrate with metals increases (Example 7), in addition, due to the roughness of the septum, the hydroxide precipitate during regeneration partially remains on the surface of the septum, i.e., the regeneration process is disturbed. When the filtering pressure is less than 0.1 MPa, the filtering speed decreases, which complicates the practical implementation of the proposed method (example 10). When the filtering pressure is more than 0.3 MPa due to excessive compaction of the sediment, at a constant filtering rate, the energy consumption for the implementation of the method increases (example 4). At an air purge pressure of less than 0.1 MPa (Example 11), as well as at a purge time of less than 10 minutes (Example 9), a precipitate in the form of a continuous layer remains on the surface of the filtering partition, i.e. the regeneration process is disrupted. When the air purge pressure is more than 0.2 MPa, the energy consumption for the implementation of the proposed method increases (example 12). An increase in the duration of air purge over 10 min does not change the moisture content of the obtained precipitate (example 6).

The selected implementation parameters of the proposed method:
the material of the filter baffle is titanium or stainless steel;
pore sizes of the filtering septum 3-5 10-15 microns;
thickness of the filtering partition up to 1.5 mm;
filtering pressure of the thickened suspension of hydroxides of 0.1-0.3 MPa;
air purge pressure through the sediment layer 0.1-0.2 MPa;
the duration of the air purge of at least 10 minutes allows you to repeatedly carry out a suspension filtering cycle;
sludge dewatering, which ensures purification of the filtrate from heavy and non-ferrous metals to a content of 0.1-0.3 mg / l (i.e., to the level of maximum permissible concentrations and below) and a precipitate of hydroxides with a moisture content of 70-75% is obtained. completely eliminates the consumption of water for the regeneration of the septum and reduces the energy consumption for the implementation of the method, since the pressure values of the filtering suspension and air purge in the proposed method are significantly lower than in the prototype.

 The proposed method is inferior to the prototype in terms of dry product productivity, referred to the unit area of the filtering partition. However, due to the fact that the implementation of the proposed method does not require any mechanical action on the precipitate, the filtering partitions of the porous metal can be compactly placed in the form of a package of sheets or disks.

Claims (1)

 METHOD FOR SILENT WASTE WATER SALTAGE CONTROL OF ELECTRICAL PRODUCTION, including filtering the sludge through a porous septum and regenerating the septum, characterized in that the sludge is filtered through a vertical porous metal partition up to 1.5 mm thick with a pore size of 3 - 15 μm under a pressure of 0.1 - 0, 3 MPa, and the regeneration of the filtering septum is carried out by blowing air through a layer of sediment on the septum under a pressure of 0.1 - 0.2 MPa with a purge time of at least 10 minutes.

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