Mechanisms of lead, copper, and zinc retention by phosphate rock

The solid-liquid interface reaction between phosphate rock (PR) and metals (Pb, Cu, and Zn) was studied. Phosphate rock has the highest affinity for Pb, followed by Cu and Zn, with sorption capacities of 138, 114, and 83.2 mmol/kg PR, respectively. In the Pb-Cu-Zn ternary system, competitive metal sorption occurred with sorption capacity reduction of 15.2%, 48.3%, and 75.6% for Pb, Cu, and Zn, respectively compared to the mono-metal systems. A fractional factorial design showed the interfering effect in the order of Pb>Cu>Zn. Desorption of Cu and Zn was sensitive to pH change, increasing with pH decline, whereas Pb desorption was decreased with a strongly acidic TCLP extracting solution (pH = 2.93). The greatest stability of Pb retention by PR can be attributed to the formation of insoluble fluoropyromorphite [Pb(10)(PO(4))(6)F(2)], which was primarily responsible for Pb immobilization (up to 78.3%), with less contribution from the surface adsorption or complexation (21.7%), compared to 74.5% for Cu and 95.7% for Zn. Solution pH reduction during metal retention and flow calorimetry analysis both supported the hypothesis of retention of Pb, Cu, and Zn by surface adsorption or complexation. Flow calorimetry indicated that Pb and Cu adsorption onto PR was exothermic, while Zn sorption was endothermic. Our research demonstrated that PR can effectively remove Pb from solutions, even in the presence of other heavy metals (e.g. Cu, Zn).     

Book reviews

ANALYTICAL PLANNING: THE ORGANISATION OF SYSTEMS

Thomas L. Saaty and Kevin P. Kearns

Pergamon Press, 1985. Price: U.S. $40.00, U.K. £29.50.

THE GEOGRAPHER AT WORK

Peter Gould

Routledge and Kegan Paul, London 1985’ Price: £8.95.

UTOPIA ON TRIAL

Alice Colman

Hilary Shipman Ltd., 19 Framfield Road, Highbury, London. May 1985 (reprinted August, 1985). Price: £7.95.

SIR RAYMOND UNWIN: ARCHITECT, PLANNER AND VISIONARY

Frank Jackson

A. Zwemmer Ltd., London 1985. 187 pp. with maps and illustrations.

STRATEGIC PLANNING IN ACTION: THE IMPACT OF THE CLYDE VALLEY REGIONAL PLAN 1946–1982

R. Smith and U. Wannop (eds)

Gower, 1985, 272 pp. Price: £16.50.

LOCALITIES, CLASS AND GENDER

The Lancaster Regionalism Group (Linda Murgatroyd, Mike Savage, Dan Shapiro, John Urry, Sylvia Walby, Alan Warde, with Jane Mark‐Lawson)

Pion Ltd., 1985. Price: £12.00.     

APPLICATION OF A LOW-FLOW ASSESSMENT MODEL FOR THE MONONGAHELA RIVER BASIN1

ABSTRACT: The application of a low-flow assessment model is illustrated for the Monogahela River Basin. The model simulates the impact of reservoir operating rules and consumptive use limitation policies on low-flow frequency at downstream locations in the basin. Policies are evaluated using an observed flow sequence and synthetic flow inputs. The paper reviews the historical development of flow management on the Monogahela to provide background for the current study.     

Relation of enhanced Pb solubility to Fe partitioning in soils

It is well documented that Pb solubility may be related to Fe chemistry in soils and enhanced Pb solubility may occur under certain reducing conditions; however, quantification of such relationships is unavailable. Based on metal classification, Pb (II) and Fe (II) are similar in some chemical characteristics. Thus, competition between Pb and Fe for ligands in soils may be important in determining Pb solubility. In this paper, Pb solubility was examined in a sandy soil after spiking with Pb and incubating for 40 days under water-flooded or non-water-flooded conditions. Solution chemistry in soil columns was adjusted using different concentrations of NaCl, CaCl(2) and deionized water of varying pH before incubation. The results showed that Pb solubility in the soil was not correlated well with pH, dissolved organic C or aqueous Fe concentrations. However, an index of Fe partition behavior using the ratio of aqueous Fe to sorbed Fe was related to Pb solubility. Enhanced Pb solubility occurred only when the index was < approximately 2 kg l(-1). The index can be a simple measure of Fe's ability to compete with Pb for ligands in solution. The ability of Fe to compete with Pb decreases as the index decreases and as the ratio approached its minimum, substantial increases in Pb solubility will be expected. In general, the index was not sensitive to changes in solution chemistry. A similar trend was observed using one data set published in the literature.     

Competitive adsorption of alkylbenzene and water vapors on predominantly mineral surfaces

Competitive adsorption of ethylbenzene (EB) and water on bentonite and of p-xylene (pXYL) and water on kaolin and silica gel was studied using a technique that allowed the amount of adsorbed water and alkylbenzene to be measured independently. EB adsorption on bentonite was not affected by water at relative humidities (RH) near 0.23 but was reduced significantly at RH's near 0.50. pXYL adsorption on kaolin and silica gel decreased with increasing RH, especially above a RH of about 0.2. Increasing RH not only decreased the amount of alkylbenzene adsorption but also resulted in a change from Type-II adsorption isotherms to ones that were essentially linear. Linear isotherms for the adsorption of hydrophobic organic compounds on hydrated soil have generally been attributed to partitioning into organic carbon (OC). However, since the clays and oxide used here had very low to trace amounts of OC, it is suggested that processes involving only mineral surfaces can give rise to linear isotherms. Based on solubility considerations alone, partitioning of EB and pXYL into adsorbed water films was not considered to be an important adsorption mechanism in this study. The effect of cation hydration on the amount of water adsorbed from a mixture of water and pXYL vapors was evaluated by comparing adsorption on Li- and Na-saturated kaolin.     

Atmospheric Emissions from Oxidation Ponds

The electrodes in industrial precipitators collect many tons of dust daily, and the efficient transfer of this dust burden to the hoppers is a challenging problem in mechanical engineering. Many varieties of devices have been tried; hammers, vibrators, scrapers, water flushing, gas blasting, etc. Impact devices for this purpose are usually called “rappers.” Laboratory experiments described in this paper show that normal (perpendicular) rapping is more effective than shear rapping; that thick dust layers are more easily removed by rapping than thin ones; that rapping becomes easier with increasing temperature, within limits; and that the electrostatic forces acting upon the precipitated dust layer play an important role. Quantitative data are shown graphically. The relation of these results to previous studies by other investigators is discussed.     

Sequential sorption of lead and cadmium in three tropical soils

It is important to examine mechanisms of Pb and Cd sorption in soils to understand their bioavailability. The ability of three tropical soils to retain Pb, Cd, and Ca was evaluated. The objectives of this study were to (1) determine the extent to which soil sorption sites are metal specific, (2) investigate the nature of reactions between metals and soil surfaces, and (3) identify how metals compete for sorption sites when they are introduced to soils sequentially or concurrently. Lead was shown to be much less exchangeable than Cd and inhibited Cd sorption. Cadmium had little effect on Pb sorption, though both Ca and Cd inhibited the adsorption of Pb at exchange sites. Lead appears to more readily undergo inner-sphere surface complexation with soil surface functional groups than either Cd or Ca. Thus, regardless of when Pb is introduced to a soil, it should be less labile than Cd.