The reactions of cadmium with calcium carbonate surfaces

The reaction of cadmium with calcite was studied with 10⁻⁶–10⁻²M Cd²⁺ using 4g CaCO₃ and 50 ml solution. The calcite-water suspension was equilibrated for 2 d before adding Cd(NO₃)₂. The CaCO₃ surface has a high affinity for Cd and at < 1 μmol g⁻¹ a linear adsorption isotherm (C-type) describes the reaction, whereas precipitation of CdCO₃ on calcite predominates at higher Cd additions. In the latter case pH decreased and solutions were undersaturated with respect to CaCO₃ indicating that CdCO₃ prevented the CaCO₃ surface from reacting with the acidity generated from CdCO₃ precipitation. The data for low Cd additions suggests that an ideal surface solid solution is formed between CdCO₃ and CaCO₃ and the Thorstenson and Plummer equation expressing the pIAP values of surface solid solutions is valid. Equilibrium was attained for low Cd additions in several minutes, whereas precipitation was a slow process; at the changeover point distinction between the two processes is difficult. The reacting surface area calculated from the maximum adsorption of Cd is 0.5-1.0 times that measured by the BET method.
The Cd-reacting surface areas of four natural calcareous minerals were much less than those found by the BET method which includes the surfaces of other minerals present. The Thorstenson and Plummer equation may be a useful way to relate solution composition and carbonate-adsorbed Cd in contaminated soils.     

Extraction of copper,lead, zinc or cadmium ions sorbed on calcium carbonate

The amount of sorbed metal ion released from CaC0₃ by 16 different extractants was found to vary with the chemical nature of the solution and the metal ion involved. In general, acid solutions dissolved a high proportion of both substrate and Cu, Ph, Cd coatings; complexing agents dissolved the same coatings but left most of the calcite; and competing cations (e.g. NH₄ ⁺, Ca²⁺) displaced primarily chemisorbed Cd and Cu. In Zn studies, little metal ion was retrieved by any extractant due to the limited solubility of the coatings formed at pH < 7.7. The diverse behavior observed in the sorption studies has been interpreted in terms of solubility and absorption equilibria. The pH of the CaC0₃ suspensions was high enough to precipitate all added Pb as hydroxy species, and excess Cu tended to precipitate at pH > 6.4 if one increased the soluble carbonate level (e.g. by adding acid). Unlike Cd and Cu, Zn was not chemisorbed; it formed sparingly soluble compounds such as ZnC0₃.2Zn(OH)₂, with excess coming out as Zn(OH)₂ at pH > 7.7. The significance of the results in respect to the mobility of metal ions in calcareous soils, and the evaluation of available levels, has been considered.     

The effects of mercury,copper, and zinc on calcium uptake by larvae of the clam,mulinia lateralis

A sensitive and rapid bioassay system using Ca-45 uptake by larvae of Mulinia lateralis as indicator is described. The values of Ca uptake per larva^?1 versus elapsed time were linear and some of the Ca uptake rates, expressed as pg Ca larva^?1 h^?1, were 148.2 (no added heavy metal), 114.4 (20 µg kg^?1 of added Hg), 89.7 (200 gg kg^?1 of added Zn) and 20.5 (40 µg kg^?1 of added Cu). Linearities were also obtained by plotting log of Ca uptake per larva^?1 against heavy metal concentrations. A new terminology, ^xCa _inf50 ^supt , was proposed which expressed the concentration of heavy metal, x, causing 50% depression of Ca uptake over the exposure time, t. For Cu, Hg, and Zn, the values of ^x Ca _inf50 ^sup72h were 18.5, 26.5 and 176.0 µg kg^?1 respectively, which were comparable to the published values of LC₅₀. The effectiveness of Ca uptake depression on a weight basis was Cu > Hg > Zn, and the same sequence was also observed for larval mortalities.     

Fortification of milk with calcium: effect on calcium bioavailability and interactions with iron and zinc

Calcium solubility, dialysability, and transport and uptake (retention + transport) by Caco-2 cells as indicators of calcium bioavailability have been estimated in the in vitro gastrointestinal digests of milk and calcium fortified milk. A significant linear correlation (p < 0.05) was obtained between calcium uptake and the amount of soluble calcium added to the cells, and also between percentage calcium uptake and the calcium measured in the analyzed samples. The solubility, dialysis, transport, and uptake values are higher (p < 0.05) for calcium fortified milks than for nonfortified milks; that is, calcium fortification increases not only calcium content but also its bioavailability. An inhibitory effect of calcium from fortified milks upon iron absorption was found. The observed effect of calcium from fortified milks upon zinc bioavailability depends on the in vitro method used, zinc solubility and dialysis decrease in calcium fortified milks, and percentage zinc uptake remains unchanged.     

Production and dissolution rates of earthworm-secreted calcium carbonate

Earthworms secrete granules of calcium carbonate. These are potentially important in soil biogeochemical cycles and are routinely recorded in archaeological studies of Quaternary soils. Production rates of calcium carbonate granules by the earthworm Lumbricus terrestris L. were determined over 27 days in a range of soils with differing chemical properties (pH, organic matter content, water holding capacity, bulk composition, cation exchange capacity and exchangeable cations). Production rate varied between soils, lay in the range $0–0.043{\text{mmol}}_{{\text{CaCO}}_3}$ (0–4.3 mg) earthworm^?1 d^?1 with an average rate of $8\times {10}^{?3}{\text{mmol}}_{{\text{CaCO}}_3}$ (0.8 mg) earthworm^?1 d^?1 and was significantly correlated (r = 0.68, P ≤ 0.01) with soil pH. In a second experiment lasting 315 days earthworms repeatedly (over periods of 39–57 days) produced comparable masses of granules. Converting individual earthworm granule production rates into fluxes expressed on a per hectare of land per year basis depends heavily on estimates of earthworm numbers. Using values of 10–20 L. terrestris m^?2 suggests a rate of $18–3139{\text{mol}}_{{\text{CaCO}}_3}{\text{ha}}^{?1}{\text{yr}}^{?1}$. Data obtained from flow-through dissolution experiments suggest that at near neutral pH, granule geometric surface area-normalised dissolution rates are similar to those for other biogenic and inorganic calcites. Fits of the data to the dissolution relationship r = k(1 ? Ω)ⁿ where r = dissolution rate, k = a rate constant, Ω = relative saturation and n = the reaction order gave values of k = 1.72 × 10^?10 mol cm^?2 s^?1 and n = 1.8 for the geometric surface area-normalised rates and k = 3.51 × 10^?13 mol cm^?2 s^?1 and n = 1.8 for the BET surface area-normalised rates. In 196 day leaching column experiments trends in granule dissolution rate referenced to soil chemistry corresponded to predictions made by the SLIM model for dissolution of limestone in soil. If soil solution approaches saturation with respect to calcium carbonate, granule dissolution will slow or even stop and granules be preserved indefinitely. Granules have the potential to be a small but significant component of the biogeochemical cycling of C and Ca in soil.     

土壤胡敏酸与铜、锌离子的络合特征及生物有效性的研究

通过田间试验研究了胡敏酸(HA)与铜、锌离子的络合特性。结果表明,施肥后土壤HA向结构复杂方向转化,HA与Cu2+、Zn2+之间的络合稳定性提高。HA-Cu2+的logk值,有机肥大于化肥;HA-Zn2+的logk值,以化肥的作用更明显。土壤HA与Cu2+或Zn2+络合,倾向于形成混合或多核络合物。施有机肥可提高HA-Cu2+或HA-Zn2+的结合强度和增加结合数量,而施化肥处理则相反。培养试验结果表明,有机肥处理的HA,玉米吸收Cu2+、Zn2+量下降,单施化肥处理下降较小;其中Cu2+吸收量受影响程度较大,而Zn2+吸收量没有那么明显。     

Distribution of copper and zinc in volcanic ashes

The distribution of copper and zinc in volcanic ashes was investigated. It was found that the total copper of volcanic ashes decreased with the increase of their total silica, showing a close relationship between the total copper and the rock types of volcanic ashes. On the other hand, the total zinc showed no such correlation with the rock types.

The contents of copper and zinc in the constituent minerals Indicated that zinc was more concentrated in the heavy minerals and was closely related to the iron contents of the constituent minerals. According to the concentrations of copper and zinc in the constituent minerals and the total contents of the minerals in the andesitic ash samples, the distribution of these elements was determined to be the following order.

Cu: volcanic glass>plagioclase>pyroxenes> titanomagnetite

Zn; pyroxenes > volcanic glass> titanomagnetite>plagioclase

Since volcanic ashes belonging to rhyolite and basalt were overwhelmingly composed of volcanic glass, it was obvious that the distribution of copper and zinc was much greater in the volcanic glass of these ashes.     

Reactions of zinc with iron-oxide coated calcite surfaces at alkaline pH

Both iron oxides and carbonate minerals, such as calcite, can sorb zinc (Zn), and therefore are important in controlling the solution concentration and availability of Zn to plants growing in calcareous soil. When present together, interactions between these components affect their sorption behaviour. We investigated changes in the reactions of Zn with calcite at alkaline pH, as the calcite surface was progressively coated by iron oxide. Coated calcite surfaces were prepared that had from 0.05 to 1.45% iron oxide. The initial concentration of Zn and the amount of iron oxide on the calcite were the most critical factors affecting adsorption, precipitation of solid phases, and the desorbability of sorbed Zn. For pure calcite at small initial Zn concentrations (< 2.5 × 10^?5 m ) adsorption was dominant; with increasing concentration, precipitation of hydrozincite (ZHC) became more important. With increasing amounts of iron oxide the amount of Zn adsorbed increased, the desorbability of the Zn decreased, and precipitation became progressively less evident, and at 1.45% iron oxide content there was no evidence of any precipitation of ZHC. The calculated maximum adsorption attributable to the iron oxide coating was inversely proportional to the thickness of the oxides on the calcite, and greatly exceeded that of iron oxide as a separate phase. The common occurrence of iron‐coated carbonates in calcareous soils and their capacity to adsorb Zn contributes to the problems of Zn deficiency, for which these soils are noted.     

Soil zinc and pH effects on leaf zinc and the interaction of leaf calcium and zinc on zinc toxicity of peanuts

Abstract

Zinc toxicity of peanuts (Arachis hypogaea L.), resulting from excessive amounts of Zn applied to previous crops, has been observed for many years in a limited number of peanut fields in Georgia. A tentative critical value of 12 mg/kg of Mehlich No.1 extractable soil Zn has been reported, but soil pH should be considered in establishing a more precise critical value since availability of soil Zn is affected greatly by soil acidity. A 3‐year study was conducted on a Tifton loamy sand (thermic, Plinthic Paleudults) to evaluate the relationship between soil pH and soil Zn on concentration of Zn in peanut leaves. Factorial treatments were 0, residual, medium, and high rates of Zn and soil pH levels near 5.5, 5.9, 6.2, and 6.8. Pod yields were not affected by treatments and Zn toxicity was not observed. Leaf Zn was affected more by soil pH than by soil Zn, but correlation coefficients were highest where both soil pH and soil Zn were included in the determination. A regression equation, based on soil pH and soil Zn, showed that an increase in soil Zn from 1.0 to 10.0 mg/kg increased leaf Zn 202 mg/kg at soil pH 4.6 and only 9 mg/kg at pH 6.6. Data from growers’ fields, in which samples were collected from eight healthy and toxic areas, indicated that a leaf Ca:Zn ratio of 50 or less was required for Zn toxicity of peanuts rather than high concentrations of leaf Zn per se.     

The chemical responses of acidic Woods Lake,NY to two different treatments with calcium carbonate

A study was conducted to compare and contrast two approaches to neutralize an acidic lake by CaCO₃ addition (Woods Lake, Adirondack Mountains, New York, U.S.A.; 42°52′ N, 71°58′ W); direct water column treatment and treatment of both the water column and sediment. The latter treatment strategy was designed to release a slow, diffusive Ca²⁺. flux across the sediment/water interface and thereby delay the rate of reacidification. Both applications satisfactorily increased the acid neutralizing capacity (ANC) and Ca²⁺ of the lake, temporarily buffering the water column pH against acidic inputs from the watershed. The water column/sediment application involved a greater (50% more) dose in order to accomplish sediment treatment and resulted in a prolonged period of positive ANC in the water column. However, both treatments neutralized approximately the same quantity of runoff and equivalence of acidic inputs. Water column/sediment treatment may be an effective approach to help delay reacidification in shallow lakes of moderate hydraulic retention times. Unfortunately, many acidic Adirondack lakes have very short hydraulic retention times (<0.5 yr) and may not be neutralized for adequate durations by either water column or water column/sediment CaCO₃ treatments.     

Effect of phosphorus,copper, and zinc addition on the phosphorus/copper and phosphorus/zinc interaction in lettuce

The effect of phosphorus (P), copper (Cu), and zinc (Zn) addition on the P‐Cu and P‐Zn interaction in lettuce (Lactuca sativa L.) was analyzed following a factorial design. The experiment was conducted in a greenhouse. Two levels of P (62 and 224 ppm), three levels of Zn (0, 0.17, and 0.34 ppm), and three levels of Cu (0, 0.03, and 0.06 ppm) were applied in all combinations to lettuce grown in perlite. The influence of the different treatments on the leaf P concentration suggests that the P‐Cu interaction was positive, whereas P‐Zn was negative. An increase in root absorption and retention and a decrease in translocation to leaves were observed for Zn and Cu when the nutrient solution was supplied at a luxurious consumption level of P.     

外源硅酸钙对棕壤基础呼吸和碳酸钙含量的影响

采用室内模拟培养的方法,研究了添加硅酸钙对棕壤基础呼吸和碳酸钙含量的影响,为土壤固碳的技术选择提供理论依据。试验设硅酸钙添加量0%、1%、2%、4%和6%5个处理。结果表明,外源硅酸钙在培养前期显著抑制土壤呼吸,其抑制程度随着硅酸钙添加量的增加而增加,平均抑制率为5%(1%处理)～12%(6%处理);整个培养期间,添加硅酸钙处理的土壤碳酸钙含量较对照显著增加,且随着添加量的增加,土壤碳酸钙含量的平均增幅从83%(1%处理)上升到398%(6%处理);土壤呼吸强度和碳酸钙含量之间符合y=Ae-Bx的指数相关关系。上述结果表明,施用硅酸钙通过促进次生碳酸盐的形成从而缓解土壤CO2释放,起到固碳减排的作用。     

土壤pH与碳酸钙含量的关系

统计分析表明,土壤pH(Y)与CaCO3含量(X)呈非线性正相关,并符合非线性回归方程Y(pH)=(a bX)/X,式中a<0,表示随着土壤CaCO3含量的增加,其pH由低而高向b值趋近;但CaCO3含量变化对pH的影响则由大变小以至消失。     

Effect of carbonate in clay fraction on fixation of zinc

The results indicate that CaCO3 in the clay fraction of Egytian soils has a greater affinity for Zn than silicate clay. Moreover, in the presence of carbonate, Zn was retained more tightly to form complexes hard to be extracted and, thus, relatively unavailable for plant uptake. Therefore, CaCO, plays an important role in zinc deficiency which is commonly found in calcareous soils.     

Abiotic degradation of lignified cell walls by carbonate and copper salt

This study reports on the destructuration of Wheat straw and Spruce wood cell walls after maceration in potassium carbonate or sodium hydroxide at pH = 10 in the presence of copper acetate. The alkaline treatments had a predominant impact on the wheat straw cell wall components over copper acetate. Either K-carbonate or Na-hydroxide extracted from wheat straw a particular lignin fraction rich in condensed C-C linkages, leading to the unmasking of new ether-linked sub-structures in the cell wall. This unmasking was increased in the presence of copper salt but only in the nonextracted Wheat straw sample incubated in carbonate and not in the corresponding extractive-free sample. This difference was related to the leaching of compounds from the nonextracted cell wall, which could sustain oxidative activity of copper by hindering its precipitation into inactive hydroxide and/or carbonate species. In Spruce wood samples, copper salt was the principal factor impacting on the lignin structure over alkali alone. Its effect was, however, only detected at the level of C-C linked dimers. These results confirmed that unmasking of lignin sub-structures also occurred in Spruce wood, but probably through mechanisms different from that evidenced in Wheat straw.     

Microbiological and chemical determination of copper and zinc in soil

Many chemical and microbiological methods to estimate the amounts of available nutrients in soil were proposed, but as a rapid laboratory method, microbiological test would appear to have advantages over chemical methods. It could be done more simply and inexpensively in various points.     

Bacterial precipitation of calcium carbonate in presence of phosphate

The formation of calcium carbonate (CaCO₃) crystals under different concentrations of K₂HPO₄ have been determined in 90 bacterial strains isolated from soil. Crystal formation decreased when PO^3?₄ ion concentration increased (in culture media) and precipitation was completely inhibited at 1.4 g I^?1 of K₂HPO₄.     

Influence of phosphate on cadmium sorption by calcium carbonate

Laboratory investigation was conducted to investigate the mechanism of cadmium sorption by pure calcium carbonate and to examine whether, reaction products of phosphate with calcium carbonate serve as a sink for sorption of toxic heavy metal cations like cadmium. The phosphatization of calcium carbonate (G.R) was carried out by treating it with orthophosphoric acid in Ca:P ratio of 5:3, 3:2, 4:3 and 1:1, representing the Ca–P ratios of carbonate apatite, tricalcium phosphate, octacalcium phosphate and dicalcium phosphate and then equilibrated for two months. The X-ray diffraction of the phosphate reaction products revealed that calcite along with monetite, brushite and carbonate apatite were present in each case. The cadmium was effectively retained on CaCO₃ by the mechanism of chemisorption at lower Cd²⁺ concentrations as the pH of the equilibrium system remained constant (8.6) up to initial Cd²⁺ concentrations of 10⁻⁴ mol, coinciding to 100% sorption of Cd²⁺ from the solution. At higher concentrations, precipitation of CdCO₃ on CaCO₃ surface or as a separate phase predominated. Enrichment of CaCO₃ with P reduced the Cd-sorption. The chemisorption of Cd probably involved the exchange of Ca²⁺ by Cd²⁺ from CaCO₃ surface. The Cd²⁺ concentration in equilibrium solution followed the solubility diagram of CdCO₃ at pH ≤ 8.6, whereas the concentration of Ca²⁺ started deviating from the solubility line at pH ≤ 8.2.     

Inhibitory effect of protein hydrolysates on calcium carbonate crystallization

Protein hydrolysates, prepared by enzymatic digestion of soybean protein and egg white albumin using several proteases, inhibited the crystal growth of calcium carbonate. Each hydrolysate showed different inhibitory activities, suggesting the key role of peptide structures in the inhibition. The deamidation of protein hydrolysates by glutaminase increased not only the inhibitory activity toward the crystal growth of calcium carbonate but also the resistance of the hydrolysates against peptic digestion. Furthermore, the addition of sodium chloride, citric acid, or lactose into the reaction mixture enhanced the inhibitory activity. The protein hydrolysates inhibited both nucleation and crystal growth of calcium carbonate and also affected the crystal morphology.     

Iron and zinc absorption characteristics and copper inhibitions in cucurbitaceae

Iron and Zn absorption, interactions, and Cu inhibitions were characterized in cucumber (Cucumis sativus L.), watermelon (Citrullus lanatus Thunb.), and pumpkin (Cucurbita moschata Poir.) by kinetic parameters V_max and K_m. Influx and V_max values for Fe and Zn absorption decreased in each species as plant age increased. For the Michaelis constant, K_m, Fe values in cucumber and watermelon and Zn values in watermelon and pumpkin were relatively unchanged with increased plant age. K_m values for Zn absorption in cucumber and Fe absorption in pumpkin decreased as plant age increased. Among species, watermelon appeared to have a particularly effective uptake mechanism for Zn at low solution concentrations. Non‐competitive inhibition of Zn absorption by Fe (20, 50 uM) was indicated in each species. Iron uptake in pumpkin was inhibited non‐competitively by Zn (5, 10 uM), however no significant effects of Zn on Fe absorption were evident in either watermelon or cucumber. Copper (0.5, 1, 5 uM) inhibited uptake of Fe non‐competitively and Zn competitively in each species.