Research On Removal Of Pollutants And Mechanism By Natural Pyrite And Pyrrhotite

The issue of environmental pollution has captured more and more attention with the development of society and the progress of civilization Permeation reaction grid technology(PRB)whose core technology is the reaction medium is a crucial in-situ remediation technology to remove heavy metals and inorganic salt pollution in groundwater.In this thesis,natural pyrite,pyrrhotite and heat-treated pyrite products were used as the reaction medium to explore their ability to remove different types of pollutants in the leachate of polymetallic mineral tailings in Guangxi and the mechanism of their reactions had also been explored.Meanwhile,their removal ability in a simulated environment was evaluated by dynamic experiments.The main achievements are as follows:(1)By using natural pyrite and pyrrhotite to remove lead,manganese,zinc and other metal cations,it was found that pyrite and pyrrhotite were able to remove lead ions under neutral conditions.But the removal effect of manganese ion and zinc ion is not perfect.At the same time,the effect of pyrrhotite in removing metal cation pollutants is slightly better than pyrite.(2)The pyrite was heat-treated under an argon protective atmosphere,and the heat treatment products at different temperatures and their changing laws were explored.The study found that the pyrite mineral phase did not change significantly at 500℃.In the range of 550℃-600℃,part of the pyrite transforms into monoclinic and hexagonal pyrrhotite.When the temperature reaches the range of 650℃-900℃ The inside is directly transformed into hexagonal pyrrhotite.(3)By Combining with static experiments,pyrite heat-treated at different temperatures were used to remove anionic pollutants such as dichromate or sulfate.Studies have found that the removal mechanism is mainly an oxidation-reduction reaction in which hexavalent chromium is reduced to low-toxic trivalent chromium and part of the divalent iron in the mineral is oxidized to trivalent iron.After the reaction,the hydroxyl oxides of chromium and iron are deposited together on the mineral surface,while the low sulfur is oxidized to sulfate ions.Moreover,it was found that the pyrite product heat-treated at 600°C had the best dichromate removal effect,reaching 6mg/g,and the possible reasons were explained.In addition,the product of heat-treated pyrite has a mediocre effect on sulfate radical removal.(4)The product of 600℃ heat-treated pyrite was selected as the reaction medium and the practical operation of PRB was simulated by dynamic column experiment.Simultaneously,the service life of PRB was evaluated and the reaction mechanism was discussed.The study found that the service life of the dynamic column in this experiment was 480 PVs.Mechanism studies have shown that the removal mechanism of dynamic experiments is still a redox mechanism and dynamic experiments are more responsive than static experiments.The above research results show that the pyrite product after proper heat treatment has a good application prospect in the absorption of chromium heavy metal pollution.