| dc.description.abstract | Previous literatures have confirmed that by moderate addition of ferrous iron and sulfate,
mercury and cadmium can be stabilized in the sediment and soil medium, and the bioavailability
of the two metals can be significantly reduced. However, the results of the previous pot
experiments in the laboratory found that only zero-valent iron can play a role in reducing the
bioavailability of cadmium in the root soil of paddy fields, while the effect of sulfate is far less
than expected. Since the subsequent investigation of bacterial species composition showed that
the proportion of sulfate-reducing bacteria in the test soil was extremely low, this study started
from the perspective of ecological redox sequence, and tried to investigate whether the reason
why sulfate could not exert its effect was the same as that in the previous period. Fertilizers
used in the experiments contained final electron acceptors that were more readily available to
local microorganisms than sulfate. In view of this, this study used the original contaminated
soil and regularly added the same amount of organic carbon (glucose and acetate) as the
measured root exudates, and divided them into groups with or without added fertilizers for a
period of two months. Soil miniature model culture experiment to explore the relationship
between (two) fertilizers, sulfate and zero-valent iron when the rhizosphere soil reaches
anaerobic state in the simulated paddy water-covered period, and the reduction of heavy metal
concentration in pore water Whether or not, as evidence of reduced bioavailability of the metal
in soil media during the test period.The results of the study found that the presence of sulfide
and ferrous iron could be successfully observed over time in soil and pore water samples
without fertilizers, and the concentration of cadmium in pore water was effectively reduced. In
the group containing fertilizer, the reduction rate of zerovalent body and sulfate was slower than
that of the group without fertilizer, and there was no response. Nitrate was detected in pore
water, and its concentration gradually decreased with time. During the process, traces of nitrite
were also found, which can confirm that the nitrate reduction (or denitrification) reaction is
going on in the system, and it can be speculated that the nitrate in the soil will compete with
zero-valent iron and sulfate, and It preferentially becomes the electron acceptor for microbial respiration in the system, and finally makes the sulfate most affected, because it cannot be effectively reduced, so that the bioavailability of cadmium in the system cannot be significantly reduced.These results indicate that when using sulfate to remediate paddy soil contaminated with cadmium or other heavy metals, it is necessary to first detect whether the fertilizer used contains a certain concentration of nitrate, because its final effect will conflict with this nitrogen fertilizer containing nitrate, and the two The result of the competition between the two in the
anaerobic rhizosphere will cause the ineffective remediation effect brought by sulfate; but if there is a lack of sufficient nitrate as an electron acceptor in the environment, the addition of sulfate still has a good effect, which can effectively reduce the amount of soil in paddy fields.Cadmium concentration in pore water, and its low price, is a soil conditioner worth considering. | en_US |