Soluble organic carbon and pH of organic amendments affect metal mobility and chemical speciation in mine soils

• Published in: Chemosphere (Oxford) 2014-05, Vol.103, p.164-171
• Main Authors: Pérez-Esteban, Javier, Escolástico, Consuelo, Masaguer, Alberto, Vargas, Carmen, Moliner, Ana
• Format: Article
• Language: English
• Subjects: Animals; Applied sciences; Biological and physicochemical properties of pollutants. Interaction in the soil; Carbon - analysis; Exact sciences and technology; Horses; Hydrogen-Ion Concentration; Manure; Metal mobility; Metals - analysis; Metals - isolation & purification; Mining; Pine bark; Pollution; Sheep; Sheep–horse manure; Soil and sediments pollution; Soil Pollutants - analysis; Soil Pollutants - isolation & purification; Solubility; Soluble organic carbon; Speciation modeling
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2013.11.055

•Manure can reduce metal availability due to high pH and degree of maturity.•Manure could increase soluble Cu at high pH because of higher soluble organic carbon.•Soluble Cu and organic carbon were minimum at pH 5.8–6.3, near pH of acid mine soils.•Manure reduced soluble Zn as it always decreased with increasing pH.•Manure reduced the predicted proportion of free metal ions in soil solution. We evaluated the effects of pH and soluble organic carbon affected by organic amendments on metal mobility to find out the optimal conditions for their application in the stabilization of metals in mine soils. Soil samples (pH 5.5–6.2) were mixed with 0, 30 and 60tha−1 of sheep–horse manure (pH 9.4) and pine bark compost (pH 5.7). A single-step extraction procedure was performed using 0.005M CaCl2 adjusted to pH 4.0–7.0 and metal speciation in soil solution was simulated using NICA-Donnan model. Sheep–horse manure reduced exchangeable metal concentrations (up to 71% Cu, 75% Zn) due to its high pH and degree of maturity, whereas pine bark increased them (32% Cu, 33% Zn). However, at increasing dose and hence pH, sheep–horse manure increased soluble Cu because of higher soluble organic carbon, whereas soluble Cu and organic carbon increased at increasing dose and correspondingly decreasing pH in pine bark and non-amended treatments. Near the native pH of these soils (at pH 5.8–6.3), with small doses of amendments, there was minimum soluble Cu and organic carbon. Pine bark also increased Zn solubility, whereas sheep–horse manure reduced it as soluble Zn always decreased with increasing pH. Sheep–horse manure also reduced the proportion of free metals in soil solution (from 41% to 4% Cu, from 97% to 94% Zn), which are considered to be more bioavailable than organic species. Sheep–horse manure amendment could be efficiently used for the stabilization of metals with low risk of leaching to groundwater at low doses and at relatively low pH, such as the native pH of mine soils.