CN1277940A - Method for purifying aluminium-poly-chloride using aluminium-carbon microeletrolysis - Google Patents

Abstract

The present invention relates to a purification method of aluminium polychloride produced from the reaction of high alumina ash with waste acid. It uses the microelectrolysis principle to produce primary battery reaction in acidic medium, the aluminium bed is composed of aluminium filings and active carbon microgranules dispersed in aluminium filings, ordinary aluminium polychloride is used as electrolyte solution. The said method can quickly and effectively remove heavy metal ions and organic matter in medium, in which the lead removal rate can up to higher than 90%. By increasing one treatment procedure and under little increase of production cost, it is realized to produce high-quality and low-impurity product with ordinary raw material.

Description

Method for purifying polyaluminium chloride by aluminium-carbon micro-electrolysis

The invention relates to a purification method of polyaluminium chloride produced by reacting high-alumina ash and waste acid, in particular to a method for removing heavy metal ions such as lead and the like and organic matters such as benzene rings and poly-benzene rings.

The process for producing the polyaluminium chloride by reacting the high-alumina ash with the waste acid has the advantages of easily available raw materials, simple equipment, low cost, high aluminum content of products and certain market advantages. However, the high-aluminaash and the waste acid have low purity, and bring a lot of harmful impurities into the product polyaluminum chloride, so the flocculant prepared by the method is generally used for industrial wastewater treatment and cannot be applied to the field of drinking water. In order to make the product suitable for drinking water plants, it is necessary to remove the harmful impurities from the polyaluminium chloride to make it meet the standards. The impurities generated by reacting high-alumina ash and waste acid to generate polyaluminium chloride mainly comprise heavy metal ions, particularly lead ions, and benzene rings and polycyclic organic matters. There are many methods for removing metal ion impurities from the aqueous solution, such as adsorption, chemical precipitation, reduction, electrochemical methods, and the like. Electrochemically removing impurities from polyaluminium chlorideExcept most effectively. Electrochemical methods for removing heavy metals include electrolysis and microelectrolysis. The electrolysis method for treating the heavy metal wastewater is the sum of various effects. Firstly, oxidation-reduction reaction occurs on an anode electrode and a cathode electrode, heavy metal ions are reduced and precipitated and attached on the electrodes because electrons obtained by the cathode, and organic matters can also react on the surfaces of the electrodes to be decomposed; secondly, if the anode adopts metal electrodes such as aluminum, iron and the like, the anode is subjected to electrochemical corrosion after being electrified and has solubility, and aluminum or iron is dissolved in solution in an ionic state and can generate hydroxyl complex through hydrolysis reaction to be used as a coagulant for coagulation treatment of suspended matters and colloids in water; thirdly, oxygen and hydrogen are generated on the surfaces of the anode and the cathode during electrolysis, and the oxygen and the hydrogen are released as micro bubbles, so that impurity particles and oil in water can be adhered tothe water surface in the rising process to float to the water surface, and the air floatation effect is generated. The electrolysis method has stable effect of treating the wastewater containing the heavy metals, simple operation and management and small occupied area of equipment, but consumes electric energy and has high operating cost. The micro-electrolysis reaction is a battery reaction which is generated by immersing substances with different electrode potentials in an electrolyte together. If the anode is a metal electrode, the anode is corroded and consumed, and is dissolved into the solution. The cathode reduces heavy metal ions into metal simple substances to be separated out, and simultaneously, H in the medium is separated out⁺Reducing into active H, so that the active H has stronger reducing capability and can perform redox reaction with a plurality of components in the solution. The micro-electrolysis method has the characteristics of wide application range, good treatment effect, long service life, low cost, convenient operation and maintenance and the like when being used for wastewater flow. The mature technology of the micro-electrolysis method for wastewater treatment is an iron bed technology. Cast iron is an alloy of iron and carbon, the composition of which is mainly pure iron and Fe₃C and some impurities. Fe₃C and other impurities are dispersed in the cast iron in the form of very small particles, which, because of their lower electrode potential than iron, form numerous corrosion microcells when in electrolyte solution, resulting in galvanic reactions. In neutral or slightly acidic environment, the cast iron electrode itself and the new ecology H, Fe generated by the cast iron electrode²⁺Etc. can undergo redox reactions with many components in the wastewater. For example, it can destroy the chromophoric group or chromophoric group of the colored substance in the colored wastewater, and can also reduce heavy metal ions, etc. Due to the fact thatUnder the action of the electric field of the battery, micro-electrolysis can reduce impurities in the aqueous solution much faster than a simple reduction method. The polyaluminium chloride prepared from the high-alumina ash contains more heavy metals, benzene rings and polyphenyl ring organic matters brought by waste acid, and the solution is acidic, so that the solution is suitable for a micro-electrolysis method, but if the traditional iron bed treatment is adopted, two defects exist: firstly, iron is brought into polyaluminium solution in the reaction, and the color and the purity of the product are influenced; second, the cathode cast iron containsThe carbon of (a) is so small that it is not conducive to having precipitated heavy metals attached to its surface, thereby affecting its removal from solution.

The invention aims to overcome the defects and provides the method for purifying the polyaluminium chloride by aluminum-carbon micro-electrolysis, which has good impurity removal effect and high product purity.

The invention changes an iron bed into an aluminum bed, uses common polyaluminium as a medium, and utilizes the potential difference between aluminum scraps and activated carbon to generate micro-electrolysis reaction in an acid medium, so that heavy metal in the common polyaluminium is separated out, and impurity organic matters are decomposed and removed by oxidation-reduction reaction. Specifically, the method for purifying common polyaluminium chloride adopts the principle of micro-electrolysis to generate galvanic reaction in an acid medium, and is characterized in that an aluminum bed is composed of aluminum scraps and activated carbon particles dispersed in the aluminum scraps, and the common polyaluminium chloride is used as an electrolyte solution. Since aluminum shavings contain little carbon, activated carbon is artificially added in a ratio,typically between 50: 1 and 10: 1, in order to create an effective, good galvanic reaction. The size of the aluminum-carbon ratio is determined according to the flow rate of liquid passing through the aluminum bed, the flow rate is large, the aluminum-carbon ratio is a little smaller value, the flow rate is small, and then the effect of taking the larger aluminum-carbon ratio is good. Because the artificial added active carbon belongs to the macroscopic category, and under the action of an electric field of a primary battery, impurity metal ions in the polyaluminium are easy to separate out and deposit on the surface of the active carbon as if a metal film is plated, the overpotential is generated after the metal film is plated on the surface of the active carbon, and the electric field generated by the primary battery increases the speed of the ions moving to a corresponding electrode, accelerates the reaction and is more favorable for the separation of the metal ions. Therefore, the method of adding the activated carbon to artificially create micro-electrolysis reaction to remove the metal ion impurities is very effective. The electrode reaction is as follows:

anode:

cathode:

(M represents a metal simple substance) of course, a plurality of organic matters are decomposed and reacted under the action of an electric field, the original structure of the organic matters is damaged, and the effects of removing color and reducing toxicity are achieved.

The common polyaluminium chloride medium forms numerous primary batteries by means of an aluminum bed formed by a certain aluminum-carbon ratio to generate micro-electrolysis reaction in an acid medium, does not contain other impurities, quickly and efficiently removes heavy metal ions and organic matters in the medium, wherein the lead removal rate is as high as more than 90 percent, the effect is very obvious, and the production of the polyaluminium chloride with high quality and low impurities from common raw materials is realized by adding one treatment process under the condition of increasing the production cost.

FIG. 1 is a chromatographic analysis of the medium before reaction in example 1.

FIG. 2 is a chromatogram of the medium after the reaction in example 2.

The present invention is further illustrated by the following examples.

Example 1 polyaluminium chloride produced by the reaction of spent acid and high alumina ash counter-currently passed through an aluminium bed at a flow rate of 1001/min, the aluminium bed consisted of aluminium scrap and activated carbon at an aluminium to carbon ratio of 10: 1, the elemental analysis before and after the reaction is shown in table one, the chromatographic analysis is shown in figure 1. As can be seen from the table I and the figure 1, the removal rate of heavy metal elements, particularly lead, is high, organic matters are also decomposed, and the content of heavy metal in the polyaluminium meets the requirement of being used in the field of drinking water after reaction.

Watch 1

Analytical elements	Ba	Ca	Cd	Co	Cr	Cu
							Before reaction (ug/g)	4.48	2.0％	0.6	11.2	8.16	336
After reaction (ug/g)	3.98	1.8％	Not detected out	Not detected out	8.16	3.67
							Analytical elements	Fe	Mg	Mn	Na	Ni	Pb
Before reaction (ug/g)	0.1％	460	212	326	Not detected out	132
							After reaction (ug/g)	928	387	57.1	459	Not detected out	Not detected out
Analytical elements	Si	Sr	Ti	V	Zn
							Before reaction (ug/g)	0.5％	28.5	408	20.4	0.20％
After reaction (ug/g)	0.45％	25.5	316	17.3	0.10％
							Note: the undetected content indicates that the element content is lower than the detection limit of the detection instrument after the sample is diluted by 100 times

In example 2, the polyaluminum chloride produced by the reaction of the spent acid and the high-alumina ash counter-currently passes through an aluminum bed at a flow rate of 401/min, the aluminum bed is composed of aluminum chips and activated carbon, the ratio of aluminum to carbon is 30: 1, and the elemental analysis before and after the reaction is shown in Table II.

Watch two

Analytical elements	Ba	Ca	Cd	Co	Cr	Cu
							Before reaction (ug/g)	4.48	2.0％	0.6	11.2	8.16	336
After reaction (ug/g)	3.77	1.8％	Not detected out	Not detected out	8.16	9.18
							Analytical elements	Fe	Mg	Mn	Na	Ni	Pb
Before reaction (ug/g)	0.1％	460	212	326	Not detected out	132
							After reaction (ug/g)	928	387	58.1	224	Not detected out	6.12
Analytical elements	Si	Sr	Ti	V	Zn
							Before reaction (ug/g)	0.5％	28.5	408	20.4	0.20％
After reaction (ug/g)	0.45％	24.4	295	18.3	989
							Note: the undetected state indicates that the content of the element is lower than the detection limit of the detection instrument after the sample is diluted by 100 times

In example 3, the polyaluminum chloride produced by the reaction of the waste acid and the high-alumina ash counter-currently passes through an aluminum bed at a flow rate of 101/min, the aluminum bed is composed of aluminum chips and activated carbon, the ratio of aluminum to carbon is 50: 1, and the elemental analysis before and after the reaction is shown in Table III.

Watch III

	Aluminum content	Basicity of salt	Pb(ppm)	Removal rate
					Before treatment	11.18％	76.73％	102.3	93.5％
After treatment	11.26％	74.63％	6.61

Claims (2)

1. A process for purifying the ordinary aluminium polychloride features that the microelectrolysis principle is used to generate primary battery reaction in acidic medium, and the aluminium bed is composed of aluminium filings and activated carbon particles dispersed in the aluminium filings, and the ordinary aluminium polychloride is used as electrolyte solution.

2. The method of claim 1, wherein the ratio of aluminum to carbon in the aluminum bed is between 50: 1 and 10: 1.

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