investigation of hexavalent chromium cr (vi) removal from contaminated clayey soil by simultaneous combination of electro kinetics and nano zero-valent iron as a permeable reactive barrier

recently, a variety of soils contaminated with heavy metals e.g. cr (vi), have been found in industrial sites. such soil contamination is widely distributed in the world and has now become a serious issue for environment. hexavalent chromium, cr (vi), which is known to be carcinogenic and mutagenic to living organisms, has been utilized for leather tanning, electroplating and in other industries. cr (vi) contaminated soil is mainly the result of improper disposal and leakage from reservoirs. accordingly, finding promising technologies to remediate cr (vi) from contaminated soils which provide high efficiency has drawn attention by many governmental officials to protect public health and the environment. this paper investigated the effectiveness of incorporating nano zero-valent iron (nzvi) into electro kinetics (ek) to remediate cr (vi) contaminated soil (100 mg/kg). the electro kinetic experiments were conducted using a 8 cm long sample under a constant electric gradient of 2 v/cm for 24 h. results from the base experiment showed that the most cr (vi) species migrated and accumulated near the anode reservoir. based upon this result a reactive barrier was installed 2 cm away the anode electrode and was filled with nzvi and silica sand (1:2.5 w/w). the cr (vi) reduction and removal efficiency for the processes with nzvi were 88% and 19, respectively. in other attempt the ph control in anode and cathode reservoirs has been considered to a value of 6.3 coupled with barrier installation near the anode reservoir to understand the effect of this phenomenon in remediation processes. since the ph control in the reservoirs promotes the release of cr (vi) from the soil by electro migration and permitting, the maximum interference with permeable reactive barrier results the increase of the removal of total cr to 42% and 89.3% reduction of cr (vi) to the cr (iii).