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Title: Transport of ARS-labeled hydroxyapatite nanoparticles in saturated granular media is influenced by surface charge variability even in the presence of humic acid

Author
item WANG, DENGJUN - Chinese Academy Of Sciences
item Bradford, Scott
item HARVEY, RONALD - Us Geological Survey (USGS)
item HAO, XIUZHEN - Chinese Academy Of Sciences
item ZHOU, DONGMEI - Chinese Academy Of Sciences

Submitted to: Journal of Hazardous Materials
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2012
Publication Date: 7/1/2012
Citation: Wang, D., Bradford, S.A., Harvey, R.W., Hao, X., Zhou, D. 2012. Transport of ARS-labeled hydroxyapatite nanoparticles in saturated granular media is influenced by surface charge variability even in the presence of humic acid. Journal of Hazardous Materials. 229-230:179-176.

Interpretive Summary: Nanoparticles (NPs) are commonly used to remediate contaminated soil and water. The objective of this research was to better understand and quantify the influence of surface charge variability on NP transport and retention under different solution ionic strength (Ic) conditions in the presence of humic acid (HA). Results indicate that HA did not completely mask the influence of surface charge variability as is commonly assumed, but rather that charge variability significantly contributed to NP aggregation and retention as the Ic increased. This information will be of interest to scientists and engineers concerned with the use of NPs to remediate polluted soil and water.

Technical Abstract: Hydroxyapatite nanoparticles (nHAP) are increasingly being used to remediate soils and water polluted by metals and radionuclides. The transport and retention of Alizarin red S (ARS)-labeled nHAP in water-saturated granular media were investigated. Experiments were conducted over a range of ionic strength (Ic, 0 to 50 mM NaCl) in the presence of 10 mg L/1 humic acid. The transport of ARS-nHAP was found to decrease with increasing suspension Ic in part, because of enhanced aggregation and chemical heterogeneity. The retention profiles (RPs) of ARS-nHAP exhibited hyperexponential shapes (a decreasing rate of retention with increasing transport distance) for all test conditions, suggesting that some of the attachment was occurring under unfavorable conditions. Surface charge heterogeneities on the collector surfaces and especially within the ARS-nHAP population contributed to the hyperexponential RPs. Consideration of the effect(s) of Ic in the presence of HA is needed to improve the efficacy of nHAP for scavenging metals and radionuclides in contaminated soils and aquifers.