| Baguan River slag field is located in the western area of Panzhihua City, and the Baguan River pass through it from north to south. The east of slag field is mountains, while its west is Panzhihua Cycas Nature Reserve, and about 300 meters distance from north to south there are residential areas. The slag field was put into use in 1993, which is the only place Panzhihua Iron and Steel Group Co. Ltd. uses to dump the blast furnace. With the capacity of Panzhihua Iron and Steel production increased, the amount of slag has been increased year by year, whose annual slag capacity is approximately 3.2 million tons and the carrying capacity is close to its limit. With lots of slag wasted abandoned here, vanadium, chromium, cadmium and other heavy metals would move into the soil, leading to the deterioration of the soil’s quality, and even doing harm to human’s health and the environment.The soil around the Baguan River slag field was chosen to be the research object in this paper, and collected samples from the upstream region, near by the slag field and the downstream region respectively, and then the pollution degree of the soil was evaluated according to the geoaccumulation index. The results showed that the soil that around the slag field was polluted seriously, which would become a potential contaminated source for the nearby residents’ safety with hidden dangers. Considered the soil has a strong self-adsorption capacity and self-purification capacity, the re-adsorption and fixation characteristics of vanadium, chromium and cadmium were mainly studied through static adsorption experiment. The principle on soil absorbing vanadium, chromium, cadmium was discussed deeply according to the characterization results of the mineral composition of the soil, characteristics of the surface charge, the content of ferromanganese aluminum oxide and the specific area and so on, and a reasonable evaluation that the potential harm the polluted soil did to the residents around here was done.As the study showed that the pollution of soil around the slag field was serious. Vanadium, chromium, cadmium in the soil showed moderate pollution in the upstream region. Around the slag field and in the downstream region, vanadium and chromium showed moderate pollution, and cadmium showed moderate pollution wild pollution.The effect of adsorption time on adsorption of vanadium showed that the vanadium absorbed by the polluted soil was very fast, and the adsorption and removal rate had a significant growth, the removal rate has increased to 90%, as a result, the adsorption time of static adsorption experiment was set to 24 hours. However, the polluted soil was tagged a moderate pollution, but it was still has better re-adsorption and self-purification for vanadium.The effect of initial concentration of the polluted liquid on the adsorption of soil showed that the overall trend of the five solid sample’s adsorption of vanadium and cadmium was increasing with the increase of the initial concentration of vanadium. When the initial concentration was up to 450mg/L, the polluted soil were still have a better adsorption-fixation ability for vanadium and cadmium,however, the soil does not have self-purification ability for chromium any more and pollution control must be carried out.The effect of p H on the soil adsorption showed that the trend of No.4 and No.15 polluted soil adsorption for vanadium decreased with the increase of p H; the adsorption of cadmium increased with the increase of p H and the adsorption of chromium had no regularities and rules.Using adsorption isotherm equation for No.4 and No.15 polluted soil adsorption for vanadium, chromium, cadmium linear fitting, the studies showed that the adsorption characteristics for the vanadium and cadmium of the two polluted soil were more in line with the Langmuir adsorption model,which was the adsorption of soil samples for vanadium and cadmium belongs to a monolayer adsorption, it is an irreversible adsorption;Two polluted soil adsorption characteristics of chromium was more in line with the Freundlich equation model, That is soil adsorption of chromium belongs to an uneven surface adsorption, it is a reversible adsorption.The XRD phase analysis results of polluted soil samples showed that the main mineral compositions of the contaminated soil samples were quartz, then it was the clay minerals. Besides, there were plagioclase, tremolite, potassium feldspar calcite and pyrite, etc. However, the clay minerals were mainly montmorillonite, illite, chlorite. At the same time, it will own positive and negative charge on the surface of the soil samples. The two kinds of charge without additive property, the positive charge was good for the soil adsorption of anions, the negative charge was beneficial to the soil adsorption of cations. The negative charge(CECp) of soil samples of permanentis mainly on account of the layered clay minerals montmorillonite, illite classes in the same as the displacement function. The positive charge(AEC) mainly originates from the clay minerals(such as montmorillonite, illite, chlorite and kaolinite) broken surface or structure layer edge octahedral structure on the surface of Al, Fe, Mn oxide hydrate or hydroxyl group.p H was the most important factor that affect the amount of positive charges and negative charges on the soil surface. In a similar p H condition, there was present a positive correlation between the adsorption quantity of VO3﹣ and the quantity of positive charge(AEC), namely with the increase of soil sample surface positive charge(AEC) in favor of adsorption- fixed of VO3﹣. The decrease of p H had advantage on the increase of charge on the surface of the soil and then helped the soil absorb VO3﹣ ions which existed in the form of negative ions, showing a large adsorption for vanadium the soil has in acidic medium. Compared with the Cr2O72-adsorption, soil had specific selective adsorption for VO3﹣. The increasing of p H had advantage on the increase of negative charge on the surface of soil and thus the adsorption of Cd2+ existing in the form of positive ions was promoted, showed an increasing adsorption of cadmium in alkaline conditions.The adsorption results of vanadium, cadmium and chromium by natural clays and purified clays showed that the purified clay had a better adsorption for vanadium and cadmium than those of natural clays, and the adsorption of chromium had no regularities and rules. Compared with natural clays, the contents of tremolite, cristobalite and albite were reduced significantly in purified clays. Although the total content of clay minerals had been increased, there were still some quartzs. Therefore, the purification method needs to be improved. The SEM and EDS analysis showed that the vanadium can be detected by spectroscopy after adsorption use NO.4 and NO.15 purified samples, which was uniform distributed and had no obvious enrichment area, but the cadmium and chromium were difficult to be detected, the main reason for those were may be the adsorption position were different. |
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