and Environmental Protection
http://ago.helion.pl ISSN 1733-4381, Vol. 12 nr 1 (2010), p-67-76
Content of heavy metals in ashes after burning biomass briquette Czop M., Kajda-Szcześniak M.,
Katedra Technologii i Urządzeń Zagospodarowania Odpadów ul. Konarskiego 18, 44-100 Gliwice
tel. +48 32 237-26-89, fax +48 32 237-11-67 e-mail: monika.czop@polsl.pl
e-mail: mkajda@polsl.pl
Streszczenie
Zawartości metali ciężkich w popiołach po spalaniu brykietów z biomasy
W artykule zaprezentowane zostały wyniki badań zawartości metali ciężkich takich jak: cynk (Zn), ołów (Pb), kadm (Cd), chrom (Cr), miedź (Cu), nikiel (Ni) oraz kobalt (Co), w popiołach powstających w wyniku procesów termicznych. Analizowane próbki popiołów stanowią pozostałość po spaleniu brykietów z biomasy, w których głównymi składnikami są słomy: owsa, pszenżyta i kukurydzy, z około 5% dodatkiem tworzywa sztucznego. Dodatek tworzywa sztucznego – polietylenu o niskiej gęstości (PE-LD), pełni funkcję materiału wiążącego w brykiecie. Prezentowane wyniki mają na celu określenie pozytywnego bądź negatywnego oddziaływania popiołów na środowisko przyrodnicze w trakcie ich składowania bądź też zagospodarowania środowiskowego poprzez wykorzystanie np. do celów budowlanych, kształtowania powierzchni gruntów, niwelacji terenów. Uzyskane wyniki badań przedstawiono w formie graficznej.
Abstract
The article presents the research of heavy metals content, such as zinc (Zn), lead (Pb), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni) and cobalt (Co), in the ashes which are created as a result of thermal processes. The analysed samples of the ashes are remains after burning biomass briquettes, which consist mainly of: oat, wheat-rye and corn with approx. 5% of the plastics. The additive of the plastics – low density (PE-LD), fulfils the function of the binding material in the briquette. The aim of the presented results is to specify positive or negative impact of the ashes on the natural environment during their storage or management by the use for, for example, construction purposes, shaping the ground area, land leveling. The results obtained are presented in graphic form.
1. Introduction
In Poland, and many other European Union countries tests are carried out on the identification of the content and side effects of the burning products (ashes and gravel) and
their significance for extending their management methods and evaluation of their impact on the natural environment.
The ashes, collected at the waste repositories are a potential source of environment pollution. Acquaintance with the physical and chemical properties, their resistance to climatic factors and erosion processes enables proper evaluation of their threat during the storage processes for the natural environment [1, 2, 3].
The amount of furnace wastes created during burning depends mainly on the quality and the caloric value of the fuels. The size and range of the impact of the furnace wastes on particular elements of environment depends on the following factors: physical and chemical properties of the wastes stored, quality of the supernatant liquids in the waste storage, waste dump structure and technology of waste storage, variations related to the processes, which take place inside the facility, morphology and hydrographics of the area, meteorological parameters of the atmospheric air and the features arising from the balance – dynamic and thermal turbulences, the storage yard area, geological structure and hydrogeological conditions of the subgrade, climatic conditions of the storage yard (mainly the amount of precipitations and temperature), ability of the environment for self-purification [3, 4, 5]. Furnace wastes are most often stored in the areas which are not prepared for this purposed and on the lands, which for their location should never be designated for storing wastes. Apart from the widely used storage method, furnace wastes are every time more often used in the industry. The main directions of the management of ashes are: use in the mining technology in the coal mines, additives to the production of cement, production of mining joint, ready-mix concrete, production of mixes for the road subbase layers, use for the recultivation of industrial and derelict areas [4, 5].
When considering an influence of the furnace wastes on the natural environment, attention should be paid to two main processes: dusting and migration of heavy metals. A direct cause for dusting of the ashes storage on waste yards is a high degree of size reduction. In the period of storing furnace wastes, dangerous materials undergo also a leaching process. They enter into various elements of the ecosystem. Often, presence of the excessive concentration of the heave metals causes negative mutagenic, teratogenic and cancerogenic effects [3, 5].
2. Testing methodology
2.1. Characteristics of samples
Testing for the thermal transformation were carried out on briquettes which consisted on the following components: oat straw, wheat-rye straw, corn straw, low density polyethylene (PE-LD), which functioned in the briquette as a binder.
The burning process was realized with the constant air flow of 15 dm3/min., in temperature of 800oC and with the exec air λ>1. The weight of briquettes was 22 g. The total time of burning process was 3480 s [6].
As a result of thermal transformation of the briquettes the following ashes samples were achieved, marked respectively:
Archives of Waste Management and Environmental Protection, vol. 12 issue 1 (2010) 69 Pr1 – Ashes from burning briquettes on the basis of oat straw and PE-LD with reduced
size, made in the temperature of 200oC and under compaction pressure of 82 MPa, Pr2 – Ashes from burning briquettes on the basis of what-rye straw and PE-LD with
reduced size, made in the temperature of 200oC and under compaction pressure of 95 MPa,
Pr3 – Ashes from burning briquettes on the basis of what-rye straw and PE-LD with reduced size, made in the temperature of 210oC and under compaction pressure of 82 MPa,
Pr4 – Ashes from burning briquettes on the basis of corn straw and PE-LD with reduced size, made in the temperature of 190oC and under compaction pressure of 82 MPa, Pr5 – Ashes from burning briquettes on the basis of corn straw and PE-LD with reduced
size, made in the temperature of 200oC and under compaction pressure of 68 MPa, Pn1 – Ashes from burning briquettes on the basis of oat straw and PE-LD with not
reduced size, made in the temperature of 190oC and under compaction pressure of 82 MPa,
Pn2 – Ashes from burning briquettes on the basis of what-rye straw and PE-LD with not reduced size, made in the temperature of 190oC and under compaction pressure of 82 MPa,
Pn3 – Ashes from burning briquettes on the basis of what-rye straw and PE-LD with not reduced size, made in the temperature of 200oC and under compaction pressure of 68 MPa,
Pn4 – Ashes from burning briquettes on the basis of corn straw and PE-LD with not reduced size, made in the temperature of 190oC and under compaction pressure of 82 MPa,
Pn5 – Ashes from burning briquettes on the basis of corn straw and PE-LD with not reduced size, made in the temperature of 200oC and under compaction pressure of 68 MPa.
2.2. Marking of heavy metals in the furnace wastes
Marking of content of heavy metals in the samples of the ashes was subject to mineralization of the samples in the nitrohydrochloric acid with the proportion of weight/volume 1 : 10. At the same time control samples were prepared.
Heavy metals (Zn, Pb, Cd, Cu, Ni, Co, Cr) were marked with the method of atomic absorption spectrometry (ASA) in the flame apparatus in the sample with the use spectrophotometer for atomic absorption, type 1100 B, Perkin Elmer.
The method of introducing the experiment for all the measurement series was the same. The results presented in the article are an arithmetic mean of three repetitions.
3. Comments on the results
The results of the performer tests are shown in drawings 1 to 7. The results obtained show that the content of particular heavy metals in the furnace wastes do not depend on the parameters of the production of briquettes (temperature oC; crush pressure MPa) and a degree of size reduction of the binder (PE-LD).
It was observed that the lowest content for the analysed samples concerns cadmium and cobalt. The level of these heavy metals did not exceed 10 mg/kg. For all the testes types of samples, the highest content was noted in zinc, lead and chromium.
The lowest zinc content of 452 mg/kg was observed in sample Pr1 (ashes from burning briquettes on the basis of oat straw and PE-LD with size reduction), and the highest in sample Pr5 (Ashes from burning briquettes on the basis of corn straw and PE-LD with reduced size) of 1720 mg/kg. Ashes achieved form burning briquettes on the basis of the polyethylene with the reduced size (Pr1 – Pr5) showed a content of lead between 71 – 140 mg/kg and chromium 38 – 410 mg/kg.
Samples of ashes, resulting from burning briquettes with the additive of polyethylene without size reduction (Pn1 – Pn5), contained lead in the amount of 22 – 308 mg/kg and chromium in the amount of 25 – 75 mg/kg.
Sample marked with symbol Pr5 (Ashes from burning briquettes on the basis of corn straw and PE-LD with reduced size) showed the highest content of copper, out of all the samples, of 95 mg/kg.
Table 3.1. Content heavy metals in the ashes resulting from burning straw
Zn Pb Cr Cu Ni Co Cd
Type of ash
[mg/kg] [mg/kg] [mg/kg] [mg/kg] [mg/kg] [mg/kg] [mg/kg] Ashes from burning
oat straw 280 42 88 48 31 6 2,0
Ashes from burning
wheat-rye straw 790 20 132 37 70 4 1,8
Ashes from burning
corn straw 2470 55 420 109 <1 9 3,5
Tested furnace wates are characterized by low content of nickel, less than 21 mg/kg, except for the sample Pr1 (ashes from burning briquettes on the basis of oat straw and PE-LD with reduced size) and Pn5 (ashes from burning briquettes on the basis of corn straw and PE-LD with not reduced size), where the amount was respectively: 43 mg/kg and 30 mg/kg. For the comparative purposes, in table 1 the results were shown for the testing of ashes resulting from burning straw.
Archives of Waste Management and Environmental Protection, vol. 12 issue 1 (2010) 71 0 200 400 600 800 1000 1200 1400 1600 1800 content of zinc [mg/kg] Pr1 Pr2 Pr3 Pr4 Pr5 Pn1 Pn2 Pn3 Pn4 Pn5
Fig. 3.1. Content of zinc in the tested ashes.
0 50 100 150 200 250 300 350 content of lead [mg/kg] Pr1 Pr2 Pr3 Pr4 Pr5 Pn1 Pn2 Pn3 Pn4 Pn5
0 50 100 150 200 250 300 350 400 450 content of chromium [mg/kg] Pr1 Pr2 Pr3 Pr4 Pr5 Pn1 Pn2 Pn3 Pn4 Pn5
Fig. 3.3. Content of chromium in the tested ashes.
0 10 20 30 40 50 60 70 80 90 100 content of copper [mg/kg] Pr1 Pr2 Pr3 Pr4 Pr5 Pn1 Pn2 Pn3 Pn4 Pn5
Archives of Waste Management and Environmental Protection, vol. 12 issue 1 (2010) 73 0 5 10 15 20 25 30 35 40 45 content of nickel [mg/kg] Pr1 Pr2 Pr3 Pr4 Pr5 Pn1 Pn2 Pn3 Pn4 Pn5
Fig. 3.5. Content of nickel in the tested ashes.
0 1 2 3 4 5 6 7 8 content of cadmium [mg/kg] Pr1 Pr2 Pr3 Pr4 Pr5 Pn1 Pn2 Pn3 Pn4 Pn5
0 1 2 3 4 5 6 7 8 9 content of cobalt [mg/kg] Pr1 Pr2 Pr3 Pr4 Pr5 Pn1 Pn2 Pn3 Pn4 Pn5
Fig. 3.7. Content of cobalt in the tested ashes.
In the analyses samples of straw high level of zinc, lead and chromium was observed. The referenced ashes are characterized with similar amounts of copper, cadmium and cobalt.
4. Summary
In order to protect the environment against the influence of the toxic components which are leached during storage of the furnace wastes, available immobilization methods should be applied. Closing heavy metals inside the crystal structures assure high resistance to penetration of the pollution into the natural environment. Solidified furnace wastes can be used in the industry: construction or mining.
Refereces
[1] Świniarski J.: Ocena emisji zanieczyszczeń ze skażonych odpadów stałych oraz gruntów za pomocą testów elucyjnych, Przegląd dotychczasowych prac naukowo- badawczych – wyniki gospodarczego wykorzystania popiołów, Prądocim 1996.
[2] Kobus A.: Monitoring lokalny środowiska w otoczeniu składowisk odpadów paleniskowych w energetyce, Energetyka nr 9, 116-124, 2000.
[3] Woźniak M., Żygadło M.: Ocena wpływu wybranych czynników klimatycznych na stabilność chemiczną odpadów paleniskowych na składowiskach mokrych, Ochrona Środowiska 2 (85), 17-21, 2002.
[4] Janigacz D.: Wpływ składowiska odpadów paleniskowych "Łęg" Zespołu Elektrowni Ostrołęka na środowisko wodne, Cz. I, Ochrona Powietrza i Problemy Odpadów 2 (35), 73-80, 2001.
Archives of Waste Management and Environmental Protection, vol. 12 issue 1 (2010) 75 [5] Adamek E., Cholewiński B., Kobus A.: Składowanie odpadów paleniskowych w aspekcie ochrony środowiska, Przegląd dotychczasowych prac naukowo-badawczych – wyniki gospodarczego wykorzystania popiołów, Prądocim 1996.
[6] Kajda-Szcześniak M.: Analiza możliwości wykorzystania wybranej biomasy w procesie formowania paliw, Praca doktorska, Politechnika Śląska, Gliwice 2008.
