Behavior of lead as a migrating pollutant in Saudi Arabian soils

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Abstract
To evaluate the capability of calcareous desert soils to minimize the migration of lead (Pb) from Pb‐containing aqueous solutions, soil from six Saudi Arabia sites were filtrated with Pb‐containing municipal solid waste (MSW) landfill leachate. Leaching continued until Pb breakthrough occurred (C/Co = 1) or 7 months’ infiltration if breakthrough did not occur, usually several hundred PVD. The effluent from (5 × 10 cm) soil columns was analyzed for selected metals and pH. Lead was strongly attenuated by all soils. Lead appeared in the effluent only after influent Fe attained a breakthrough. Calcium was negatively attenuated. Only Onaiza sand and Buraida sand reached their maximum Pb‐holding capacity (i.e., a complete Pb breakthrough). As a result of removing the soil from the columns in 2‐cm segments, lead was found to be almost evenly distributed throughout the columns. A dominant fraction of the attenuated Pb was readily extracted by 0.1 N HCl. The attenuation data behaved according to the Freundlich and the Langmuir adsorption isotherms, suggesting the prominence of Pb sorption over other mechanisms. Kharj sand and Quatif sandy loam retained the highest quantity of Pb, though allowing some to pass through, thus indicating multiple reactions of sorption, precipitation, chelation, and organic complexation. This was demonstrated by nonconformity of the data to normal Freundlich or Langmuir isotherms. Hasa and Deerab loams retained all the Pb of the 0‐ to 2‐cm layer. Only 11% was acid extractable. Attenuation was correlated mostly with particle size and lime. The following regression equation (R2 = 0.967) roughly estimates how far aqueous Pb‐bearing solutions will migrate through these six arid‐land soils: Z = Pb retained, as percent of the total added C = clay + percent silt Y = percent CaCO3 + percent CaSO4 Thus the longevity of Pb occlusion appears to be related to the migration and/or de sorption of CO3 2‐ in the soil system.