Method for removal of metal ions from rice hull

Abstract

A method for removal of metal ions from rice hulls. The method includes: 1) providing a water storage reactor, and disposing a gas dispersion device at the bottom of the water storage reactor; 2) bagging rice hulls, placing it in the water storage reactor, and pressing down on the bagged rice hulls to be lower than a water surface in the water storage reactor; 3) spraying industrial flue gas into the water storage reactor; controlling the amount of the industrial flue gas such that about 1 g of carbon dioxide is dissolved per 100 g of water, thus generating a carbonic acid solution; 4) allowing the carbonic acid solution to react with metal ions in the rice hulls to yield a precipitate; and 5) washing the rice hulls collected in step 4), washing again with desalinated water, and then squeezing the rice hulls.

Claims

1. A method for removal of metal ions from rice hulls, the method comprising: 1) providing a water storage reactor, disposing a gas dispersion device at the bottom of the water storage reactor, and filling the water storage reactor with water; 2) placing the rice hulls in a bag and placing the bag in the water storage reactor, and submerging the bag in the water; 3) bubbling industrial flue gas into the water via the gas dispersion device; controlling the amount of the industrial flue gas such that about 1 g of carbon dioxide is dissolved per 100 g of water, thus generating a carbonic acid solution; 4) reacting the carbonic acid solution with metal ions in the rice hulls to yield acidified rice hulls and a precipitate; and 5) washing the acidified rice hulls to remove the precipitate and to yield washed rice hulls, and then squeezing the washed rice hulls to remove the metal ions from the washed rice hulls.

2. The method of claim 1, wherein the water storage reactor has a depth of between 6 and 10 m.

3. The method of claim 2, wherein the gas dispersion device comprises a gas orifice configured to horizontally or vertically agitate water to form vortexes, and the industrial flue gas is sprayed from the gas orifice.

4. The method of claim 3, wherein the gas orifice is at least 1.5 m higher than the bottom of the water storage reactor.

5. The method of claim 4, wherein the gas orifice has a pore size of between 0.005 and 0.012 mm.

6. The method of claim 3, wherein the gas dispersion device further comprises a plurality of microporous aerators, and the industrial flue gas is sprayed from the microporous aerators.

7. The method of claim 5, wherein the gas dispersion device further comprises a plurality of microporous aerators, and the industrial flue gas is sprayed from the microporous aerators.

8. A method for removal of metal ions from rice hulls, the method comprising: 1) providing a reaction tank, the reaction tank comprising a gas distributor disposed at a lower part thereof and a liquid distributor disposed at an upper part thereof, wherein the gas distributor comprises microporous aerators, a recycle liquid outlet is disposed on a wall of the reaction tank below the gas distributor, a gas outlet is disposed at the top of the reaction tank, and a precipitate outlet is disposed at the bottom of the reaction tank; 2) filling the reaction tank with the rice hulls and water, closing the gas outlet, and spraying industrial flue gas from the microporous aerators of the gas distributor; 3) dissolving carbon dioxide in the industrial flue gas into the water at 4 g of carbon dioxide per 100 g of water, to yield a carbonic acid solution; 4) reacting the carbon acid solution with metal ions of the rice hulls to yield acidified rice hulls and a precipitate; and 5) washing the acidified rice hulls to yield first washed rice hulls, washing the first washed rice hulls with desalinated water to yield second washed rice hulls, and then squeezing the second washed rice hulls to remove the metal ions from the second washed rice hulls.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a sectional view of a water storage reactor in according to one embodiment of the invention;

(2) FIG. 2 is a top view of a water storage reactor in FIG. 1; and

(3) FIG. 3 is a sectional view of a reaction tank in according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(4) For further illustrating the invention, experiments detailing a method for removal of metal ions from rice hulls by utilizing industrial flue gas are described below. It should be noted that the following examples are intended to describe and not to limit the invention.

Example 1

(5) As shown in FIGS. 1-2, a method for removal of metal ions from rice hulls by utilizing industrial flue gas is described as follows.

(6) 1. A water storage reactor 1 having a depth of 7 m and a length and width respectively of 100 m was provided. 25 gas dispersion devices 2 for introducing industrial flue gas were disposed at the bottom of the water storage reactor 1. The gas dispersion devices 2 comprised a gas orifice (not shown in the drawings) configured to horizontally or vertically agitate water to form vortexes. The industrial flue gas was sprayed from the gas orifice. The gas orifice was 1.5 m higher than the bottom of the water storage reactor, and had a pore size of 0.01 mm. The gas dispersion devices 2 further comprised a plurality of microporous aerators, and the industrial flue gas was sprayed from the microporous aerators.

(7) 2. The rice hulls 5 was bagged, placed in the water storage reactor 1, and pressed down using press bars to be lower than the water surface of the water storage reactor.

(8) 3. The industrial flue gas released from a biomass power plant was filtered by dust collecting equipment, and received by a gas main 4 which was connected to the gas dispersion devices. The industrial flue gas was sprayed into the water with depth of 5.5 m via the gas dispersion devices 2. Under such conditions, the dissolution amount of carbon dioxide in the water was increased by 5 folds compared with that under normal temperature and pressure, that is, 1 g of carbon dioxide was dissolved per 100 g of water. Thus, a carbonic acid solution was obtained, which was adapted to acidify the rice hulls 5. The metal ion of the rice hulls reacted with the carbonic acid solution to yield a precipitate. Thereafter, the rice hulls 5 were washed, and squeezed with desalinated water, whereby removing the metal ion from the rice hulls 5.

(9) Besides the precipitate, the acidification of the rice hulls also produced a solution. The solution was rich in nitrogen, phosphorus, potassium, sodium, and small organic molecules. The precipitate was mainly a carbonate and oxide of a metal such as aluminum, calcium, magnesium, iron, and manganese. The insoluble substances and the dust in the industrial flue gas precipitated in the bottom of the water storage reactor. The treatment period for the rice hulls lasted for 6 days. Then, the rice hulls were washed twice, and then desalinated water added, and squeezed. After such steps, between 60 and 75% of metal ions were removed. For each cycle, the treatment amount of the rice hulls can reach about 2500 tons.

Example 2

(10) As shown in FIG. 3, a method for removal of metal ions from rice hulls by utilizing industrial flue gas is described as follows.

(11) A reaction tank 13, having a height of 15 m and an inside capacity of 1000 m.sup.3, was provided. A gas distributor 7 comprising microporous aerators was disposed at the lower part of the reaction tank 13. A recycle liquid outlet 6 was disposed on the wall of the reaction tank 13 below the gas distributor 7. A gas outlet 10 was disposed at the top of the reaction tank 13, and a cone was disposed at the bottom of the reaction tank for collecting precipitates. At the bottom of the cone, a precipitate outlet 8 was disposed. A demister 12 and a liquid distributor 11 were disposed at the upper part of the reaction tank 13. The demister 12 was disposed above the liquid distributor 11.

(12) Firstly, the reaction tank 13 was filled with rice hulls and water. The rice hulls were floated on the water surface, and was below the liquid distributor 11. The gas outlet 10 was closed. The industrial flue gas was sprayed from the microporous aerators of the gas distributor 7. Under such conditions, the pressure of the industrial flue gas in the reaction tank 13 increased rapidly. The dissolution amount of carbon dioxide in the water was increased by 20 folds compared with that under normal temperature and pressure, that is, 4 g of carbon dioxide was dissolved per 100 g of water. Thus, a carbonic acid solution was obtained, which was adapted to acidify the rice hulls 5. The carbonic acid solution was sprayed on the rice hulls 5 from the liquid distributor 11, so that the metal ion of the rice hulls reacted with the carbonic acid solution to yield a precipitate. Thereafter, the rice hulls 5 were washed, and squeezed with desalinated water, whereby removing the metal ion from the rice hulls 5.

(13) After such steps, 80% of metal ions were removed. For each cycle, the treatment amount of the rice hulls can reach about 100 tons.

(14) If the water storage reactor 1 in Example 1 and the reaction tank in Example 2 were combined for use, that is, the water storage reactor 1 is used for primary treatment, and the reaction tank 13 is used for secondary treatment, and the resulting rice hulls are washed and squeezed using desalinated water thrice, then 90% of metal ions are removed.

(15) Metal residues in the rice hulls after being treated by method in Example 1, Example 2, and a combination thereof, are listed in Table 1.

(16) TABLE-US-00001 TABLE 1 Components (%) Metal Sample Elements SiO.sub.2 Al Fe Mn Mg Ca Cu Zn Ti K Na others content Raw rice hulls Content 80.5 3.80 0.44 0.2 2.71 3.56 0.027 0.003 0.31 2.8 1.53 4.12 15.38 Method in Example 1 (wt. %) 88.3 1.3 0.2 0.1 1.0 1.1 0.025 0.002 0.2 1.4 1 2.4 6.33 Method in Example 2 94.7 0.7 0.18 0.06 0.5 0.6 0.015 0.001 0.15 0.5 0.6 2 3.30 Combination thereof 97.5 0.4 0.1 0.03 0.2 0.2 0.01 0 0.1 0.2 0.3 1 1.54

(17) As shown in the above table, the method of the invention exhibits the same removal effect of metal ions from rice hulls by utilizing industrial flue gas as by utilizing strong acid, and the resulting rice hulls can absolutely meet the requirement for preparation of silica for a biomass power plant.

(18) Unless otherwise indicated, the numerical ranges involved in the invention include the end values.

(19) While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.