Heavy metal adsorbing agent and method of using same

An agent for adsorbing and preventing leakage of heavy metals in the industrial waste, etc. includes coral sand of 60 mesh or less. The coral sand can be heated in the atmosphere of reduced pressure, vacuum or argon or nitrogen gas, or air dried in order to accelerate activation of coral sand.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to heavy metal adsorbing agent, and more 
particularly to an agent for adsorbing heavy metals contained in 
industrial waste so that soil, ground water, rivers, etc. can be prevented 
from being contaminated by the heavy metals. 
2. Prior Art 
Today's industrial and technological development causes several problems. 
One of them is heavy metal pollution derived from industrial waste. 
Presently, the amount of industrial waste has significantly increased, and 
the disposition of industrial waste is one of the most vital issues in the 
industry. There are several ways to dispose of the industrial waste. One 
is to bury the waste in the soil and the other is to burn the waste into 
ash and dump the ash in remote mountains or disposition factories. 
However, industrial waste can contain a great amount of heavy metal which 
can be easily dissolved in water. In this regard, rain contributes to the 
heavy metals dissolving, and undergound water is thus easily contaminated 
by the dissolved heavy metals. The underground water flows out with rain 
and as a result causes industrial pollution in rivers, etc. 
One measure presently taken to solve the problem is to remove the 
contaminated soil and replace it with clean soil. However, the removed 
soil is still regarded as industrial waste since it contains heavy metals. 
Thus, the removed soil causes another problem: it is hard to find a place 
to dispose of it, and the disposal of the contaminated soil is very 
costly. 
An attempt has been made to use zeolite as a heavy metal adsorbing agent so 
that replacement of contaminated soil with clean soil will no longer be 
necessary. However, zeolite does not have a high adsorption ratio against 
the heavy metal ions; therefore, the use of zeolite is not an effective 
way to prevent heavy metal pollution. 
SUMMARY OF THE INVENTION 
In view of the above, the inventor of this application conducted several 
different experiments in order to solve the problems caused by heavy 
metals. 
As a result, the inventor discovered that coral sand has a high adsorption 
effect of heavy metals contained in the industrial waste. 
The inventor further discovered that a substance including coral sand and 
an aggregation agent is most suitable as an agent for adsorbing heavy 
metals contained in the soil. 
Therefore, the primary object of the present invention is to provide an 
agent for adsorbing heavy metals which includes coral sand. 
In keeping with the principles of the present invention, the objects of 
this invention are accomplished by using coral sand as an agent for 
adsorbing heavy metals contained in the industrial waste so that the heavy 
metals can be prevented from leaking out of contaminated soil.

DETAILED DESCRIPTION OF THE INVENTION 
The coral sand used in the present invention is obtained from live corallum 
(skeleton) of reef-building coral. The coral sand contains calcium 
carbonate (CaCO.sub.3) as a main component (approximately 95%). It also 
includes magnesium, strontium, sodium, potassium, phosphorus, and 
chlorine, and a small amount of iron, copper, zinc, manganese, cobalt, and 
chromium as essential inorganic elements. These elements are accumulated 
and weathered by the life activities of reef-building coral, which is 
Coelenterata. 
The coral sand is extremely porous. When a piece of coral sand is examined 
with a microscope, innumerable holes of 10-50 microns in diameter can be 
observed. The holes open evenly at the edges of the coral sand like the 
holes of a lotus root. Thus, the coral sand has excellent porosity and an 
extremely broad surface area. 
As seen in the above, since the coral sand has an extremely broad surface 
area, it can easily adsorb various kinds of heavy metal ions. 
As for the relationship between the surface area and the adsorption effect, 
the broader the surface of the coral sand, the higher the adsorption 
effect can be. Thus, in the present invention natural coral sand is 
processed into a fine powder form to increase the surface area. It is 
preferable to pulverize the coral sand into 60 mesh or less. Further, when 
the coral sand is washed so that elements such as salt, etc., which stick 
to the coral sand, is removed, activation of the coral sand can be higher 
and the heavy metal adsorption effect of the coral sand can be improved. 
It is also effective to heat and activate the coral sand up to 200.degree. 
to 450.degree. C., preferably 250.degree. to 350.degree. C., under reduced 
pressure, or under a vacuum, or in an argon or nitrogen gas atmosphere. 
The coral sand can be dried in the air for the same purpose. 
The description below demonstrates one of the ways to use the agent of this 
invention: First, dig a hole where industrial waste will be disposed and 
place the agent of this invention in the hole. After applying a heat 
treatment etc. to the industrial waste to convert it into ash, put the ash 
into the hole. Cover the ash with the agent of this invention. These steps 
are repeated such that the agent of the invention and the industrial waste 
in a manner of ash are layered one on top of the other. In this manner, 
the heavy metal in the industrial waste is adsorbed by the chemical agent 
of this invention. 
Referring to FIG. 2, the description below demonstrates another one of the 
ways to use the agent of this invention: First, dig a hole 1 in the earth 
where industrial waste will be disposed and line the hole 1 with a liner 
made from a water impervious sheet material such as rubber and place the 
agent 7 of this invention in the hole 1. After applying a heat treatment 
etc. to the industrial waste to convert it into ash 8, put the ash 8 into 
the hole 1. Cover the ash 8 with the agent 7 of this invention. These 
steps are repeated such that the agent 7 of the invention and the 
industrial waste in a manner of ash are layered one on top of the other. A 
drain pipe is then provided in the lowest point of the hole 1 and source 
of water represented by water pipe 6 is provided to run water into the 
agent 7 and ash 8 which is layered in the hole 1. Accordingly, the water 
collected in the drain pipe 5 contains almost no heavy metals; however, if 
further filtering is desired, a coral sand filter 9 can be provided in the 
drain pipe 5. In addition, the function of the water pipe 6 can be taken 
over by natural rainfall if desired. In this manner, the heavy metal in 
the industrial waste is adsorbed by the chemical agent 7 of this 
invention. 
Thus, the soil where the industrial waste is deposited can be cleaned and 
as a result can be used for various kinds of effective and useful 
purposes. Since the heavy metal adsorbing agent of the present invention 
uses natural substance, i.e. coral sand, the cost of disposing of the 
industrial waste can be kept very low. 
In order to prove the adsorption effects of coral sand, tests were 
conducted to compare it to zeolite. 
TEST RESULTS 
Prior to the primary comparison test, an analysis of acid soluble heavy 
metals and heavy metals which can be liquated (liquatable heavy metal) was 
carried out for the soil collected. 
I. Analysis Results for Contaminated Soil 
1. Site for Collection and Method Used for the Analysis 
The contaminated soil was collected in a housing development located at 
3-chome, Hasune, Itabashi-ku, Tokyo, Japan. In particular, nine (9) spots 
were selected, and after stirring and mixing the soil of 50 cm square and 
15 cm deep at each spot, about 1 kg of soil was collected. The soil thus 
collected was dried by air. Then, the soil was sieved completely by using 
a 1 mm sieve so that it was ready to be used for later analysis. 
2. Acid soluble Heavy Metal Analysis Results 
For the nine samples collected, an analysis of acid soluble cadmium (Cd), 
lead (Pb), zinc (Zn), nickel (Ni), copper (Cu), manganese (Mn), chromium 
(Cr), mercury (Hg) and arsenic (As) was conducted, respectively. 
(i) Method for Analysis: 
a. Decomposition of samples: Pb was decomposed by aqua regia-perchloric 
acid, and the others were all decomposed by mixed three types of acids 
(perchloric acid:nitric acid:sulfuric acid=20:5:1). 
b. Measurement of respective elements: All measurements were conducted by 
using the atomic absorption method. 
However, for background correction, Shimazu's highly sensitive mercury 
analysis device (MA-610) was used for Hg, Shimazu's highly sensitive 
arsenic analysis device (ASA-1) was used for As, and a heavy hydrogen lamp 
was used for all of the other remaining elements. 
(ii) Results of Analysis 
The results of analysis of the heavy metals which are decomposable by acid 
obtained from the nine samples are as shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Analysis Results for Heavy Metals Decomposable by Acid 
Unit: ppm per dry soil 
Cu Zn Mn Cr Cd Pb Hg Ni As pH 
__________________________________________________________________________ 
1 142 599 
980 63.6 
2.7 
472 0.81 
40.0 
9.5 
5.05 
2 141 721 
647 164 3.2 
1367 1.11 
53.0 
15.2 
5.44 
3 151 657 
906 74.2 
6.4 
3058 0.61 
45.1 
11.9 
5.59 
4 99.5 
310 
647 58.9 
1.6 
398 0.89 
34.0 
6.5 
6.23 
5 134 367 
799 70.2 
1.1 
405 1.21 
39.4 
8.5 
7.38 
6 99.2 
267 
932 49.1 
1.09 
39.9 
0.23 
34.9 
8.8 
8.63 
7 108 567 
856 348 48.7 
1616 0.04 
35.8 
7.1 
6.45 
8 111 594 
653 86.4 
9.7 
568 1.44 
28.6 
7.0 
7.13 
9 285 662 
1565 
153 5.3 
466 1.61 
50.4 
18.2 
4.87 
__________________________________________________________________________ 
3. Results of Analysis of Liquefactive (water soluble) Heavy Metals 
For the nine samples collected, the analysis for the heavy metals which can 
be eluted (liquated or water soluble) was conducted. 
The nine types of elements subjected to the analysis were the same as those 
for the analysis of acid soluble heavy metals. 
(i) Method for Analysis 
a. Extraction of respective heavy metals: 50 ml of distilled water was 
added to 5.0 g of air-dried soil, and after shaking for four hours, 
dry-filtration was performed using filter papers (No. 5C). The filtrate 
thus obtained was used for the test. 
b. Measurement of heavy metals: All measurements were conducted using the 
atomic absorption method. However, 
Hg, and As were measured by the same methods as that used for the acid 
soluble heavy metals. 
Cd, Pb, and Zn were measured by the direct method using hydrogen-air flame 
(The background was corrected by the heavy hydrogen lamp). 
Mn, Ni, Cu, and Cr were measured by the flameless method (A graphite 
heating furnace was used) (The background was corrected by the heavy 
hydrogen lamp). 
(ii) Results of Analysis 
The results of analysis of the nine types of heavy metals which can be 
liquated are shown in Table 2. 
TABLE 2 
______________________________________ 
Analysis Results for Water Soluble Heavy Metal 
pHCu Zn Mn Cr Cd Pb Hg Ni As 
______________________________________ 
1 7.65 0.10 
0.06 0.13 0.04 0.03 0.03 N.D. N.D. N.D. 
2 7.00 0.00 
0.10 0.78 0.05 0.00 0.00 N.D. N.D. N.D. 
3 7.00 0.10 
0.06 0.04 0.05 0.05 0.00 N.D. N.D. N.D. 
4 7.25 0.01 
0.02 0.29 0.01 0.02 0.00 N.D. N.D. N.D. 
5 7.70 0.02 
0.02 0.05 0.03 0.00 0.02 N.D. N.D. N.D. 
6 7.95 0.00 
0.03 0.00 0.03 0.00 0.00 N.D. N.D. N.D. 
7 8.20 0.05 
0.02 0.02 0.60 0.03 0.01 N.D. N.D. N.D. 
8 8.05 0.02 
0.05 0.00 0.39 0.02 0.00 N.D. N.D. N.D. 
9 8.25 0.15 
0.06 0.04 0.07 0.03 0.00 N.D. N.D. N.D. 
______________________________________ 
Unit: ppm per dry soil 
(Note) N.D.: 
Hg0.01 ppm 
As0.01 ppm 
Ni0.1 ppm 
(iii) Heavy Metal Content in Sample Soil 
In the analysis results of the acid soluble heavy metals for the nine soil 
samples, Cr exceeded the pollution criterion [criterion was based upon the 
full analysis results (the data was provided by the Public Pollution 
Affairs Section of Ward Office of Itabashi-ku, Tokyo)] in seven samples 
except those soil samples labeled No. 1 and 4, Cd exceeded the pollution 
criterion in sample No. 7, and Pb exceeded the pollution criterion in 
sample Nos. 2, 3 and 7. 
However, the amount of the respective types of heavy metals eluted was very 
small according to the elution analysis. Except that 0.6 ppm and 0.4 ppm 
(about 1/10 of the reference value) of Cr was detected in sample Nos. 7 
and 8, respectively, the amount of eluted heavy metals was approximately 
less than one several tenth of the contaminated soil criteriion value in 
every sample. 
It is assumed that most of the heavy metals contained in the soil are 
present in an insoluble state in water or hardly soluble in water. 
II. Test for Comparing the Effects or Coral Sand and Zeolite 
At first, it was planned to carry out the above-mentioned test using the 
most heavily contaminated samples of soil collected from the housing 
development. However, as mentioned above, only a small amount of eluting 
heavy metals was detected from each of the samples. Therefore, it was 
inappropriate to use these soil samples for the test. 
Consequently, contaminated soil containing a certain amount of heavy metals 
which can be liquated was assumed, and the eluted solution obtained by 
eluting the assumed soil with distilled water was prepared artificially 
(hereinafter called "artificially contaminated soil extract"). Using this 
artificially contaminated soil extract, two types of tests were conducted 
as follows. 
1. Shaking Treatment Test 
(i) Polluted Soil Assumed to Contain the Water Soluble Heavy Metals Ten 
Times the Quantity of Criterion (by Public Pollution Affairs Section of 
Itabashi-ku Ward Office in Tokyo) Based on the Elution Analysis for 
Contaminated Soil 
As the reference values according to the elution analysis results for 
contaminated soil, which are set by the Public Pollution Affairs Section 
of the Ward Office of Itabashi-ku, Tokyo, Hg: 0.05 ppm, Cd: 1.0 ppm, Pb: 
10.0 ppm, Cr(VI): 5.0 ppm, As: 5.0 ppm are given. 
Based on the above, by assuming the soil contains heavy metals ten times 
the quantity of the reference value, the artificially contaminated soil 
extract obtained from the soil assumed as mentioned above was prepared. 
Elution was carried out using distilled water ten times the quantity of the 
soil. The concentrations of the respective heavy metals in the extract 
obtained were as shown below. 
Cu: 10 ppm, Zn: 10 ppm, Mn: 10 ppm, Cr(III): 10 ppm, Cd: 1.0 ppm, Pb: 10 
ppm, Hg: 0.05 ppm, As: 5 ppm, pH: 5.00. 
As to Cu, Zn, Mn, Cr(III), and Ni, because the reference value is not set, 
10.0 ppm the same as that of Pb was applied. Cr(VI) was left out as it was 
not removed by coral sand (tested previously). 
TEST METHOD 
Coral sand and zeolite in the amount of 1 g and 2 g were added respectively 
to 50 ml each of artificially contaminated soil, and the mixtures were 
left for one night and stirred at intervals. Then, they were shaken for 
four hours using a shaker. 
After measuring the pH of the suspensions, dry-filtration was performed 
using No. 5C filter paper, and nine types of metals were measured for the 
filtrates obtained. 
The coral sand was supplied by the Bureau of Environmental Protection of 
the Tokyo Metropolitan Government Office, and zeolite was from a mine in 
Miyagi prefecture of Japan. The coral sand and zeolite used in the test 
were ground to be 60 mesh or less in size. 
TEST RESULTS 
The test results are shown in Table 3. In the Table, the elimination ratio 
was calculated from the following equation. 
Elimination Ratio (%)=A 
Concentration of each metal in artificially contaminated soil extract=B 
Concentration of each metal in treated filtrate=C 
EQU A(%)=(B-C)X(100/B) 
TABLE 3 
__________________________________________________________________________ 
Shaking Test Results 
Unit: Measured value = ppm 
Elimination Ratio = % 
__________________________________________________________________________ 
Cd Zn Pb Mn Ni 
Treating Measured 
Elimination 
Measured 
Elimination 
Measured 
Elimination 
Measured 
Elimination 
Measured 
Method 
pH Value Ratio Value Ratio Value Ratio Value Ratio Value 
__________________________________________________________________________ 
Not 5.00 
1.00 -- 10.0 -- 10.0 -- 10.0 -- 10.0 
Treated 
Zeolite 
1.0 g 
5.05 
0.81 19 8.34 17 0.82 92 8.58 14 8.61 
2.0 g 
5.10 
0.76 24 7.26 21 0.21 98 7.67 23 7.54 
Coral 
sand 
1.0 g 
8.00 
0.02 98 0.07 99 0.00 100 3.85 62 4.86 
2.0 g 
8.05 
0.01 99 0.00 100 0.00 100 1.76 82 3.63 
__________________________________________________________________________ 
Ni Cr(III) Cu Hg As 
Treating Elimination 
Measured 
Elimination 
Measured 
Elimination 
Measured 
Elimination 
Measured 
Elimination 
Method 
pH Ratio Value Ratio Value Ratio Value Ratio Value Ratio 
__________________________________________________________________________ 
Not 5.00 
-- 10.0 -- 10.0 -- 0.050 -- 5.00 -- 
Treated 
Zeolite 
1.0 g 
5.05 
14 0.27 97 5.35 47 0.033 34 4.42 12 
2.0 g 
5.10 
25 0.00 100 4.12 59 0.030 40 3.71 26 
Coral 
sand 
1.0 g 
8.00 
51 0.00 100 0.29 97 0.005 90 4.03 19 
2.0 g 
8.05 
65 0.00 100 0.18 98 0.008 84 4.09 18 
__________________________________________________________________________ 
(ii) Polluted Soil Assumed to Contain the Water Soluble Heavy Metals in 
Amount Equivalent to Reference Value Based on Elution Analysis Results for 
Polluted Soil 
By assuming the contaminated soil containing the water soluble heavy metals 
in the amount equivalent to the reference value based on the elution 
analysis results, the artificially contaminated soil extracts containing 
the respective types of heavy metals as shown below were prepared, and the 
same shaking test as in (i) was conducted for them. 
It was confirmed in the previous test that the effect of zeolite was 
conspicuously inferior to that of coral sand. In this test, the treated 
material was limited to coral sand. 
TEST METHOD 
50 ml of artificially contaminated soil extract containing Cd-1; As-0.5; 
Hg-0.05; Pb, Zn, Ni, Cu, Mn, Cr(III)-1 each (unit is ppm for all of them), 
0.25 g, 0.50 g 0.75 g, and 1.00 g of coral sand of 60 mesh or less in size 
was added. While stirring at intervals, the respective mixtures were left 
for one night, then shaken for four hours using a shaker at room 
temperature. 
After measuring the pH of the suspensions (mixtures), dry-filtration was 
conducted by using the No. 5C filter paper, and each heavy metal in the 
filtrates thus obtained was measured. 
TEST RESULTS 
Measured values and the elimination ratios obtained are as shown in Table 
4. 
TABLE 4 
__________________________________________________________________________ 
Shaking Test Results 
Unit: Measured value = ppm 
Elimination ratio = % 
__________________________________________________________________________ 
Cd Zn Pb Mn Ni 
Treating Measured 
Elimination 
Measured 
Elimination 
Measured 
Elimination 
Measured 
Elimination 
Measured 
Method 
pH Value Ratio Value Ratio Value Ratio Value Ratio Value 
__________________________________________________________________________ 
Not 5.80 
0.100 -- 1.00 -- 1.00 -- 1.00 -- 1.00 
Treated 
Coral 
sand 
0.25 g 
9.15 
0.001 99 0.00 100 0.00 100 0.10 90 0.02 
0.05 g 
9.10 
0.001 99 0.01 99 0.00 100 0.06 94 0.02 
0.75 g 
9.10 
0.001 99 0.00 100 0.00 100 0.04 96 0.01 
1.00 g 
9.00 
0.001 99 0.00 100 0.00 100 0.03 97 0.00 
__________________________________________________________________________ 
Ni Cr(III) Cu Hg As 
Treating Elimination 
Measured 
Elimination 
Measured 
Elimination 
Measured 
Elimination 
Measured 
Elimination 
Method 
pH Ratio Value Ratio Value Ratio Value Ratio Value Ratio 
__________________________________________________________________________ 
Not 5.80 
-- 1.00 -- 1.00 -- 5.00 -- 0.50 -- 
Treated 
Coral 
sand 
0.25 g 
9.15 
98 0.01 99 0.01 99 1.05 79 0.33 34 
0.50 g 
9.10 
98 0.01 99 0.00 100 0.73 85 0.43 14 
0.75 g 
9.10 
99 0.00 100 0.01 99 0.73 85 0.39 22 
1.00 g 
9.00 
100 0.00 100 0.01 99 0.73 85 0.41 18 
__________________________________________________________________________ 
The summary of the results obtained by the tests (i) and (ii) are as 
follows: 
For the respective heavy metals, the effect of zeolite is far inferior to 
that of coral sand. 
Coral sand is higher in effectiveness with regard to increasing the pH of 
the extract. 
Cd, Zn, Pb, Cu and Cr can be removed almost completely (95% or above in 
elimination ratio) with 1.0 g of coral sand when the content is ten times 
the quantity of the reference value. They can be removed nearly completely 
by 0.25 g of coral sand when their content is equivalent to the reference 
value each. 
The material in quantity of 0.25 g against 50 ml of the extract corresponds 
to 5% of the soil in ratio. 
With regard to Mn and Ni, when their contents are ten times the reference 
value each, they cannot be removed by coral sand. When the content is 
equal to the reference value, at least 30% each of them can be removed by 
treatment with 0.25 g or more of coral sand. 
To Hg, coral sand is more effective than zeolite. 
About 10-20% of Arsenic, or As, can be removed by coral sand. 
2. Impregnation Test 
(i) Test Method 
A glass column 11 mm in inner diameter is filled with coral sand so that 
the thickness is 4 cm (that is, 2.0 g each). From the top of the column, 
the artificially contaminated soil extract [(the solution used in shaking 
test ii)] prepared by assuming the contaminated soil containing the water 
soluble heavy metals in a quantity equivalent to the reference value 
according to the liquation analysis results was dropped. For the treated 
liquid (about 30 ml was obtained after two days) which flowed down to the 
bottom portion of the column, nine types of heavy metals were measured. 
In comparison with the shaking test, this test can be regarded as being 
closer to reality. (The sketch illustrating the test apparatus is shown in 
FIG. 1.) 
(ii) Test Results 
The measured values and the elimination ratios obtained for the respective 
heavy metals are as shown in Table 5. 
TABLE 5 
__________________________________________________________________________ 
Impregnation Test Results 
Unit: Measured Value = ppm Elimination Ratio = % 
__________________________________________________________________________ 
Cd Zn 
Meas- Elimi- 
Meas- 
Elimi- 
Pb Mn Ni 
ured nation 
ured nation 
Measured 
Elimination 
Measured 
Elimination 
Measured 
Elimination 
Samples 
pH Value Ratio 
Value 
Ratio 
Value Ratio Value Ratio Value Ratio 
__________________________________________________________________________ 
Stock 
5.85 
0.10 -- 1.00 -- 1.00 -- 1.00 -- 1.00 -- 
solution 
Coral 
7.90 
0.003 97 0.00 100 0.05 95 0.00 1.00 0.00 100 
sand 
__________________________________________________________________________ 
Cr Cu Hg As 
Measured 
Elimination 
Measured 
Elimination 
Measured 
Elimination 
Measured 
Elimination 
Samples 
pH Value Ratio Value Ratio Value Ratio Value Ratio 
__________________________________________________________________________ 
Stock 
5.85 
1.00 -- 1.00 -- 5.00 -- 0.50 -- 
solution 
Coral 
7.90 
0.01 99 0.02 98 0.62 88 0.17 66 
sand 
__________________________________________________________________________ 
The results obtained are summarized as follows: 
A complete removal of Hg and As was not obtained by coral sand. 
The remaining five types of heavy metals was removed nearly 100% by coral 
sand. 
III. Summary and Conclusion 
As a material for turning the heavy metals to be hardly soluble in water, 
zeolite is noticeably inferior to coral sand. 
Coral sand is highly effective in elevating the pH of the extract from the 
soil. 
With respect to Cd, Pb, Zn, Ni, Mn, Cu, and Cr even from the contaminated 
soil with elution criteria in their contents, they can be almost 
completely removal via the covering up treatment with coral sand (60 mesh 
or less in size) of 4 cm or more in coating thickness. 
As mentioned above, the agent according to this invention comprising coral 
sand has an excellent heavy metal ions adsorbing property. It prevents the 
heavy metal from leaking out of dump site of industrial waste, and 
therefore, the ground water and soil can be kept clean. Therefore, it is 
possible to use the dump site of industrial waste in effective and useful 
purposes. Further, since the agent of this invention is made of natural 
substances, the manufacturing cost can be low.