CN105661267B - Heavy metal reduction method for grains - Google Patents

Abstract

The invention relates to the field of food processing and quality safety control, in particular to a heavy metal reduction method for grains. The method comprises the steps of washing the grains with water, washing with an acid-alcohol solution, washing with salt water, finally washing with water, filtering out washing wastewater, performing sedimentation separation, and recovering residues containing heavy metals. The grain washing machine carries out low-pressure vacuum washing and high-pressure washing on grains, is beneficial to loosening tissue structures and washing out heavy metals, adopts an acid-alcohol solution, is beneficial to dissolving glutelin and prolamin, releases combined heavy metal ions, removes the heavy metals from washing wastewater in a settling mode and the like, recycles the heavy metals eluted from washing liquor, can recycle the washing liquor, and is beneficial to saving energy and reducing consumption.

Description

Heavy metal reduction method for grains

Technical Field

the invention relates to the field of food processing and quality safety control, in particular to a heavy metal reduction method for grains.

Background

In recent years, with the rapid development of industries, mining industries, non-ferrous metal smelting industries and metal product industries, the soil heavy metal pollution area is gradually increased and the pollution degree is increased. Cadmium pollution of agricultural products such as rice seriously threatens grain safety and human health. However, the polluted cultivated land is difficult to control and repair in a short time, so that the cadmium standard exceeding problem of rice produced every year is prominent.

At present, the measures for reducing the cadmium pollution of rice at home and abroad mainly focus on controlling the biological accumulation of cadmium in rice, including phytoremediation and removal of cadmium in rice field soil; the change of the existing form of cadmium in the paddy soil reduces the migration and bioavailability of the cadmium; and (3) cultivating a new rice variety with low cadmium enrichment capacity. However, polluted cultivated land in rice planting areas in China is difficult to restore in a short period, so that the problem of excessive cadmium in rice production is increasingly prominent. Researchers at home and abroad try to improve the processing precision, ferment, acidolyze and the like to remove cadmium from the polluted rice, promote the research and development of the cadmium-removing clean processing technology of the rice, but stay in the research stage of laboratories. At present, an efficient, environment-friendly and large-scale cadmium-polluted rice clean treatment engineering technical system is not formed in China, and the cadmium-polluted rice still seriously threatens the health and the grain safety of people.

Heavy metals are mainly present in a tightly bound form with proteins, phytic acid, cellulose and the like in grains. In order to remove heavy metals from grains, the molecular chains of the bound heavy metals need to be opened, and the binding of the heavy metals and molecules needs to be destroyed.

Disclosure of Invention

the invention mainly aims to provide a heavy metal reduction method for grains, and provides a heavy metal reduction method for grains, which is low in cost, strong in operability and high in efficiency.

The technical scheme of the invention is as follows:

A method of heavy metal abatement of grain, the method comprising the steps of:

1) Washing grains with water, and filtering washing wastewater to obtain a material 1;

2) Carrying out acid-alcohol cleaning on the material 1, and filtering cleaning wastewater to obtain a material 2;

3) Washing the material 2 with water, and filtering washing wastewater to obtain a material 3, wherein the material 3 is the heavy metal reduced grain;

4) Collecting the cleaning wastewater obtained in the step 2) and the step 3), performing sedimentation separation, and recovering the residue containing heavy metals.

The acid-alcohol cleaning method in the step 2) is to add 1.5-5 times of the volume of the grain, and clean for 0.1-5 min under the pressure of 0.01-0.099 MPa; and then cleaning for 0.1-2 min under the condition that the pressure is 0.1-0.3 MPa, alternately performing for 1-5 times, wherein the operation temperature is-20-55 ℃, and then filtering out cleaning wastewater.

And the acid alcohol solution obtained in the step 2) is prepared by adding organic acid or inorganic acid into alcohol to obtain 0.05-0.5 mol/L acid alcohol solution.

The organic acid is citric acid, lactic acid, acetic acid, tartaric acid, malic acid or their combination, the inorganic acid is hydrochloric acid, phosphoric acid or sulfuric acid, and the alcohol is ethanol.

The water cleaning method in the step 3) is to add water with the volume of 1.5-5 times of that of the grains and treat the grains for 0.1-5 min under the pressure of 0.01-0.099 MPa;

then treating the wastewater under the pressure of 0.1-0.3 Mpa for 0.1-2 min, alternately performing 1-5 times at the operation temperature of-20-55 ℃, and then filtering the cleaning wastewater.

And 4) the cleaning wastewater is subjected to sedimentation separation, namely, the cleaning wastewater is collected, a heavy metal complexing agent is added, the mixture is uniformly stirred and kept stand for 65-75min, and the separation is carried out, wherein the separation method comprises gravity sedimentation or centrifugal sedimentation (centrifugal force is 10-1000g, and 0.5-30min) or filtration, so that heavy metal-containing residues are obtained.

the heavy metal complexing agent is polyaluminium chloride, carboxymethyl chitosan, quick lime or a combination thereof, is in a powder or pellet shape, has the particle size of 0.1-1mm, is added in an amount of 10-200 mg/L, and can be repeatedly used.

The heavy metal is cadmium, lead, aluminum, mercury or a combination thereof.

The grain is rice or wheat or millet or corn or coix seed or bean or powder thereof, and the grain size is 0.01-20 mm.

The invention provides a heavy metal reduction method for grains, which has the following beneficial effects:

1. the invention firstly washes the grains, which is beneficial to the relaxation of the tissue structure and the washing out of heavy metals;

2. The invention adopts the acid-alcohol solution, which is beneficial to dissolving and releasing the combined heavy metal ions of the glutelin and the alcohol soluble protein, and removes the heavy metal from the material by settling and other modes;

3. According to the invention, water cleaning is carried out after acid and alcohol treatment, low-pressure treatment and high-pressure treatment are alternately carried out, wherein high pressure is favorable for loosening the grain tissue structure, washing liquid permeates into grains, and low pressure is favorable for transferring heavy metal ions to the outside, so that the heavy metal ions can be thoroughly removed;

4. The invention can recycle the heavy metal eluted from the washing liquid, and the washing liquid can be reused, thus being beneficial to energy conservation and consumption reduction;

5. The invention has reliable technical process and good effect; the heavy metal content of the grains treated by the method is lower than the national standard.

Detailed Description

The invention is further illustrated by the following examples, but the scope of the invention as claimed is not limited to the scope of the examples.

Example 1 optimal heavy metal reduction method for cereals

500g of rice is added, and the weight of the rice is 500g,

1) washing rice with water, and filtering washing wastewater to obtain a material 1;

2) Cleaning the material 1 with acid-alcohol solution, and filtering cleaning wastewater to obtain a material 2;

3) Washing the material 2 with water, and filtering washing wastewater to obtain a material 3, wherein the material 3 is the heavy metal reduced rice;

4) Collecting the cleaning wastewater obtained in the step 2) and the step 3), performing sedimentation separation, and recovering the residue containing heavy metals.

The water washing method of the step 1) is to add water with the volume 3 times that of rice, wash for 3min under normal pressure, with the operation temperature of 25 ℃, and then filter out washing wastewater.

The acid-alcohol solution cleaning method in the step 2) is to add acid-alcohol solution with the volume 3 times that of rice and process for 3min under the pressure condition of 0.03 MPa;

Then treating for 2min under the pressure of 0.2MPa, alternately performing for 3 times, wherein the operating temperature is 25 ℃, and then filtering out the cleaning wastewater.

The water cleaning method of the step 3) comprises the steps of adding 3 times of rice volume of water, treating for 2min at the pressure of 0.03MPa, treating for 2min at the pressure of 0.15MPa, alternately performing 3 times, and filtering out cleaning wastewater, wherein the operation temperature is 25 ℃.

The acid-alcohol solution obtained in the step 2) is prepared by adding citric acid into 70% (V/V) ethanol solution to prepare 0.03mol/L acid-alcohol solution.

And the method for carrying out sedimentation separation on the cleaning wastewater in the step 4) comprises the steps of collecting the cleaning wastewater in the step 2) and the step 3), adding 350g of polyaluminum chloride, uniformly stirring, standing for 20min, and filtering to obtain heavy metal-containing residues and clean washing water.

detecting the heavy metal content of the rice before and after the heavy metal reduction, and measuring: the cadmium content of the raw material rice is 0.36mg/kg, and the cadmium content of the cleaned material (material 3) is 0.13 mg/kg. The cadmium content of the dry clean washing water is 0.02 mg/kg.

Example 2 Effect of acid alcohol washing on grain heavy Metal abatement

The cadmium content of the rice after cleaning was measured by changing the parameters of the low-pressure vacuum cleaning in the acid-alcohol cleaning in the step 2) and using the parameters in table 1 with the materials and method of example 1.

TABLE 1 Effect of acid alcohol cleaning on heavy Metal abatement of cereals

Serial number	Pressure, MPa	time, min	Cadmium content, mg/kg
				1	0.099	3	0.21
2	0.08	3	0.17
				3	0.06	3	0.15
4	0.03	3	0.14
				5	0.06	5	0.14

As can be seen from Table 1, the cadmium content of the (material 3) after the washing is reduced with the increase of the pressure, which indicates that the first low-pressure vacuum washing is firstly carried out in the acid-alcohol washing process, which is beneficial to the relaxation of the tissue structure and the washing out of heavy metals.

Example 3 Effect of different concentrations of acid alcohol on cereal heavy Metal reduction

The materials and methods of example 1 were used except that in step 2) the acid alcohol concentration was as shown in Table 2.

TABLE 2 Effect of acid alcohol concentration on cereal heavy Metal reduction

As can be seen from Table 2, the adoption of the acid-alcohol solution is beneficial to dissolving gluten and alcohol soluble protein to release combined heavy metal ions, heavy metal is removed from the material in a settling mode and the like, the influence of alcohol concentration and acid concentration on cadmium removal effect and rice sensory quality is large, when the alcohol concentration is 50-70% and the acid concentration is proper, sufficient cadmium removal can be ensured, and the rice sensory quality is excellent.

Example 4 comparison of cadmium removal Effect of several acid-alcohol solutions

The materials and methods of example 1 were used, but the acid types in table 3 were used.

as can be seen from Table 3, the cadmium removing effect of different kinds of acids on cereals is different, wherein the cadmium removing effect of citric acid, lactic acid, acetic acid and hydrochloric acid is better than that of phosphoric acid and sulfuric acid.

TABLE 3 comparison of cadmium removal effectiveness of several acid-alcohol solutions

Serial number	Acid name	concentration, mol/L	Cadmium content, mg/kg
				1	citric acid	0.1	0.15
2	lactic acid	0.1	0.18
				3	Acetic acid	0.1	0.19
4	Hydrochloric acid	0.1	0.19
				5	Phosphoric acid	0.1	0.21
6	sulfuric acid	0.1	0.22

example 5 separation of heavy Metal residue in cleaning waste Water

using the materials and methods of example 1, the amounts of polyaluminum chloride recovered from heavy metals with the cleaning waste liquid removed were as shown in Table 4.

TABLE 4 influence of polyaluminium chloride dosage on cadmium content of cleaning effluent

Serial number	Polyaluminum chloride, mg/L	Clean washing water cadmium content, mg/L	Aluminum content of clean washing water in mg/L
				1	10	0.0002	0.001
2	50	0.0001	0.002
				3	90	0	0.003
4	150	0	0.002
				5	200	0	0.001

(national standard drinking water < 0.2mg/L, cadmium < 0.005mg/L)

As can be seen from Table 4, the invention can recover and treat the heavy metals eluted from the washing liquid, basically and thoroughly recover the cadmium in the washing liquid, ensure the reutilization of the washing liquid, and is beneficial to energy conservation and consumption reduction.

Example 6 reduction Effect of heavy metals in Coix seed flour

500g of coix seeds are adopted and crushed into powder with the grain size of about 80-120 meshes, and then the method of the embodiment 1 is used for cleaning (material 3) to obtain the cadmium content of 0.02mg/kg, the lead content of 0.012mg/kg and the mercury content of 0.003 mg/kg.

the cadmium content of the raw material coix seed is 0.16mg/kg, the lead content is 0.068mg/kg, and the mercury content is 0.007 mg/kg.

Example 7 cadmium removal efficiency of corn grits

The raw material adopts corn grits with the particle size of 1 mm-4 mm, and the method of the embodiment 1 is adopted to measure that: the content of cadmium in the raw material corn grits is 0.29mg/kg, and the content of cadmium in the cleaned material (material 3) is 0.16 mg/kg. The cadmium content of the dry clean washing water is 0.03 mg/kg.

the above-described embodiments are merely preferred embodiments of the present invention, and should not be construed as limiting the present invention, and features in the embodiments and examples in the present application may be arbitrarily combined with each other without conflict. The protection scope of the present invention is defined by the claims, and includes equivalents of technical features of the claims. I.e., equivalent alterations and modifications within the scope hereof, are also intended to be within the scope of the invention.

Claims (1)

1. A method for heavy metal abatement of grain, the method comprising the steps of:

1) washing rice with water, and filtering washing wastewater to obtain a material 1;

2) Cleaning the material 1 with acid-alcohol solution, and filtering cleaning wastewater to obtain a material 2;

3) Washing the material 2 with water, and filtering washing wastewater to obtain a material 3, wherein the material 3 is the heavy metal reduced rice;

4) collecting the cleaning wastewater obtained in the step 2) and the step 3), performing sedimentation separation, and recovering heavy metal-containing residues;

The water cleaning method in the step 1) is to add water with the volume 3 times that of rice, wash for 3min under normal pressure, with the operation temperature of 25 ℃, and then filter out cleaning wastewater;

The acid-alcohol solution cleaning method in the step 2) is to add acid-alcohol solution with the volume 3 times that of rice and process for 3min under the pressure condition of 0.03 MPa;

treating under 0.2MPa for 2min, alternately performing for 3 times at 25 deg.C, and filtering to remove cleaning wastewater;

the water cleaning method of the step 3) comprises the steps of adding 3 times of rice volume of water, treating for 2min at the pressure of 0.03MPa, treating for 2min at the pressure of 0.15MPa, alternately performing for 3 times, wherein the operation temperature is 25 ℃, and then filtering out cleaning wastewater;

Adding citric acid into 70% (V/V) ethanol solution of the acid-alcohol solution obtained in the step 2) to prepare 0.1 mol/L acid-alcohol solution;

and the method for carrying out sedimentation separation on the cleaning wastewater in the step 4) comprises the steps of collecting the cleaning wastewater in the step 2) and the step 3), adding 350g of polyaluminum chloride, uniformly stirring, standing for 20min, and filtering to obtain heavy metal-containing residues and clean washing water.