Comparison between acidulation by sulfuric acid and by phosphoric acid for Saudi phosphate rock

A detailed investigation of two phosphate rock acidulation modes has been carried out in batch acidulators. The classical dihydrate process rate is affected by the coating of the rock particle by gypsum. The clean phosphoric acid process using phosphoric acid as an acidulation agent does not suffer from this inhibitory coating effect, however it is affected by the increasing viscosity of the solution during acidulation. Under practical conditions the rate of acidulation using phosphoric acid is much higher than that of the dihydrate process using sulfuric acid as an acidulation agent.     

盐酸酸化磷矿生产氮磷复合肥的研究

介绍用盐酸酸化磷矿粉生产氮磷肥的方法.按生成CaHPO4化学计量加入盐酸,反应完成后,加入硫酸铵进一步转化CaHPO4和CaCl2得到无水氮磷肥,该肥料中的磷几乎全部以水溶性P2O5存在.氮磷肥可作为基肥生产三元复混肥.     

Obtaining NPK fertilizers using decomposition of phosphate rock by sulphuric acid

In this study a method for obtaining granular NPK fertilizers of various grades has been established. Kola apatite or Baltic phosphorites were dissolved in 57% H₂SO₄; the resulting slurries were then ammoniated, evaporated and mixed with urea or ammonium nitrate and potassium salts. In some experiments micronutrients (B, Cu, Mo, Co or Mn) were added. The mixtures were dried and granulated. When using urea, granulation was carried out by heating the mixture until partial melting occurred, but the mixtures with ammonium nitrate had to be granulated with the addition of water. The products contained 29–38% fertilizer nutrients (N soluble in water, P₂O₅ soluble in citric acid and K₂O soluble in water) and had a ratio of over 90% of P₂O₅ soluble in citric acid to the P₂O₅ total. The granules were hygroscopic, but little caking occurred. The urea-containing materials produced better granules. Adding micronutrients usually resulted in an improvement in the product quality (an increase in the granule hardness and phosphorus solubility).     

The agronomic value of products resulting from the partial acidulation of North Carolina phosphate rock with phosphoric acid

The influence of differing degrees of phosphoric acid acidulation of North Carolina phosphate rock on the total P uptake of ryegrass was examined. The fertilisers were applied at three rates, using two granule sizes, to three soils in pots in the glasshouse.Similar results were obtained in the three soils. Increase in P rate applied increased total P uptakes. Increase in degree of acidulation increased P content of the foliage and the smaller granules also gave slightly higher values in two soils.Except in one soil, using the smaller granules, there appeared to be no contribution of P for plant growth from the unreacted rock component of the fertilisers.     

Partial acidulation of an ‘unground’ phosphate rock: II. Plant availability of phosphate

Four greenhouse experiments were conducted using three soils to determine the availability to plants of P from unground North Carolina phosphate rock (PR) treated with 20% to 50% of the H₃PO₄ required for complete acidulation. The influences of soil P retention, P status, the method of preparation of partially acidulated phosphate rocks (PAPRs) and the granule size of the products were investigated. Perennial ryegrass was grown as the test plant for up to 8 months. Triple superphosphate (TSP) was used as the standard fertilizer and unground North Carolina rock was included for comparison.The dry matter yield and P uptake response curves showed that in all experiments PAPRs were markedly superior to the PR. P status of soils appeared to influence the effectiveness of PAPRs to a greater extent than P retention. In soils of low P status the degree of acidulation required for PAPR to be nearly or as effective as TSP was 50% whereas in a soil of high P status even 30% PAPR applied as a maintenance fertilizer was effective. There was a significant positive correlation between water soluble P of fertilizers and P uptake by ryegrass. However, in general PAPRs were more effective per unit of water soluble P than TSP. Granule size (< 1 mm and 1–2 mm) and method of preparation of PAPRs did not alter the effectiveness of PAPRs.     

Phosphate rock and phosphate rock/sulphur granules as phosphate fertilizers and their dissolution in soil

A field trial was conducted for 3 years to evaluate phosphate rocks and phosphate rock/sulphur granules as fertilizers for permanent pastures. Two reactive phosphate rocks, North Carolina (USA) and Chatham Rise (New Zealand), and an unreactive Florida (USA) were used. The materials were applied to a highly phosphate retentive allophanic soil of medium to high phosphorus status. Single superphosphate was employed as the standard fertilizer. The fertilizers were applied at four rates including a control in the first year and again in the third year. The field design enabled measurement of residual effects as well. All the plots received blanket applications of sulphate. The rate of dissolution of phosphate rock was measured by determining soil inorganic phosphate fractions at the highest rate of fertilizer application.The reactive phosphate rocks applied with or without sulphur were as effective as superphosphate in the first and third year of the trial respectively under low and medium responsive conditions. The Florida rock was at the best only 55% as effective as superphosphate. When applied after granulating with sulphur the value increased to 72%. In the second year there was no greater residual effect from the phosphate rocks compared with superphosphate. However, in the third year reactive phosphate rocks gave a slightly greater residual effect; averaged over rates of application the yield increase was 23% over control compared with 18% for superphosphate.The reactive phosphate rocks, applied with or without sulphur, dissolved at the rate of 44% of that added in the first year and 62% of that remaining in the second year. The corresponding values for Florida rock were 27% and 30%, and for Florida with elemental sulphur 35% and 33%. Over 3 years about 96% of the reactive rocks dissolved compared with 56% and 78% in the case of Florida and Florida with sulphur respectively.     

Agronomic evaluation of fertilizers with special reference to natural and modified phosphate rock

Most of the phosphate fertilizes currently used worldwide (16 million tonnes of P) are water soluble. Direct application of phosphate rock accounts for just 3.5%. Since most phosphate rock is used to produce water-soluble phosphate fertilizer, about 150 million tonnes of byproduct phosphogypsum are produced annually on a worldwide basis. This has given rise to concerns about its management and disposal in an environmentally acceptable manner. Despite the small amount of phosphate rock presently used for direct application, its use is becoming increasingly common in the developing countries, especially Latin America, due to the high cost of water-soluble phosphate fertilizers and to the variety of soils, crops and climatic conditions of the region. Agronomic effectiveness of phosphate rocks has been measured by the concept of Relative Agronomic Effectiveness where the yields are compared to those obtained with Triple Superphosphate (TSP) or Diammonium Phosphate (DAP). Phosphorus uptake as a response of the phosphate rock applied is measure by tissue analysis. This methodology is already standard for the member countries of the Latin America Phosphate Rock Network.     

Long-term greenhouse evaluation of partially acidulated phosphate rock fertilizers

The agronomic effectiveness (yield and P uptake) of twelve granular, partially acidulated phosphate rock fertilizers (PAPR) and two finely ground, unacidulated phosphate rocks (PR) were compared to that of a single superphosphate in a long-term greenhouse experiment with lucerne (Medicago sativa L., cv. CUF101), grown in a low P sorbing, moderately acid, sandy loam soil of moderate P status (Paleustaf). The PAPRs were prepared from two unreactive PRs (Christmas Is. A grade and Duchess rock from Queensland) and acidulated at two rates (25% and 50% on a H₂SO₄ to single superphosphate basis) with either H₂SO₄ or H₃PO₄. Additional products included H₂SO₄ PAPRs cogranulated with elemental S (10% w/w).Superphosphate was consistently superior to all PRs and PAPRs in agronomic effectiveness throughout this two-year study. The most effective of the PAPRs were those that were 50% acidulated with H₂SO₄ and cogranulated with elemental S; this type of fertilizer from both rocks was approximately 2/3 as effective as superphosphate when relative agronomic effectiveness indices (RAE) were calculated from cumulative yields. The increase in agronomic effectiveness relative to superphosphate (RAE value) by the partial acidulation of the PR could be attributed to its effect of increasing the P solubility in the PAPR. A curvilinear relationship existed between the RAE values of PRs and PAPRs, measured from cumulative yield or P uptake data, and the percentage of the total P in each fertilizer that was in a soluble (water + citrate soluble) form. Cogranulation with elemental S (10% w/w) significantly displaced this relationship upwards by increasing the RAE of H₂SO₄ PAPRs by more than 50%. The maximum cumulative recovery of applied P by lucerne tops after five bulked harvests (fifteen consecutive harvests) was 61.5%, which occurred at the low application rate of superphosphate. The decline in the substitution value of PRs for superphosphate, that occurred with increasing P rates tended to be offset both by increasing the level of acidulation and by cogranulating the PAPR with elemental S.     

Long-term greenhouse evaluation of partially acidulated phosphate rock fertilizers

Twelve granular partially acidulated phosphate rock (PAPR) fertilizers were compared with unacidulated phosphate rocks (PR) and superphosphate at five rates of total P in the presence and absence of supplementary sulfate and plant residue recycling treatments in a long-term green-house experiment with lucerne (Medicago sativa L., cv. CUF101). The PAPRs were prepared from two PRs (Christmas Is. A grade and Duchess, Queensland) and acidulated at two rates (25% and 50% on an H₂SO₄ to single superphosphate basis) with either H₂SO₄ or H₃PO₄. Six harvests (each bulked from three cuttings) were collected over a 2-year period. It was generally found that lucerne response to PAPRs depended closely on their water-soluble plus citrate-soluble P contents which increased with increased degree of acidulation. The H₃PO₄ tended to yield more soluble P on acidulation of PR than H₂SO₄ and acidulation of Christmas Is. PR yielded more soluble P than did acidulation of Duchess PR. There was little evidence for enhanced availability of P due to action of the triple point solution in hydrolyzing granules on residual PR in those granules.     

Partial acidulation of an ‘unground’ phosphate rock: I. Preparation and characteristics

Partially acidulated phosphate rocks were prepared from unground North Carolina phsophate rock and H₃PO₄ by (i) mixing phosphate rock with the requisite amount of H₃PO₄, (ii) mixing with a portion of the acid followed by adding the remaining acid during granulation and (iii) single-step acidulation and granulation. The degrees of acidulation were 20, 30, 40 and 50%. Only 20% and 30% acidulations were done by method (iii). The phosphate rock granulated readily on addition of H₃PO₄ either as in method (ii) or (iii) and the products did not need external drying before storage. The citric and water soluble P showed that from the viewpoint of acid-phosphate rock interaction all three methods of preparation were satisfactory. The granules were equally strong as or stronger than commercially available single or triple superphosphate samples tested. The percent degradation on abrasion was less than 4% compared to about 8% for superphosphate and 0.4% for triple superphosphate. A sand incubation study suggested an interaction in the partially acidulated phosphate rock between the monocalcium phosphate component and unreacted phosphate rock which initially increased the solubility of P.     

Evaluation of soil phosphate status where phosphate rock based fertilizers have been used

Soil phosphorus (P) tests have usually been calibrated using regression relationships between test values and crop yields for soils with a history of soluble P fertilizer use. However, the regression relationships have frequently been found to be different where phosphate rock (PR) based fertilizers have been used. Consequently, the traditional soil P tests often give incorrect estimates of soil P status of PR fertilized soils where calibrations were derived using soils treated with soluble P fertilizers. Alkaline soil tests (e.g., Olsen, Colwell) usually underestimate, while acid tests (e.g., Truog, Bray 2) usually overestimate, the soil P status of PR fertilized soils where normal calibrations are used. Several ways of overcoming this problem are discussed. Separate calibrations can be used for soluble and PR based fertilizers. In practice, this could involve mathematical modification of test values obtained with PR fertilized soils to enable use of the normal calibrations. Soil and fertilizer P models are available which use fertilizer history to derive current fertilizer recommendations and/or predict consequences of different fertilizer strategies. These could be extended to include functions describing the dissolution of PR in soil. This requires more detailed information on PR dissolution rates in different soils. Two soil tests for use with both soluble P and PR fertilized soils have recently been developed. They are the iron-oxide impregnated paper and the mixed anion exchange membrane/cation exchange membrane tests. While more evaluation is required in field situations, evidence to date indicates that both tests show promise.     

Reactive rock phosphate fertilizers and soil testing for phosphorus: The effect of particle size of the rock phosphate

North Carolina rock phosphate (NCRP) (highly carbonate—substituted apatite) was ground to produce three samples with different particle size distributions. The effectiveness of these fertilizers was compared with the effectiveness of superphosphate in a field experiment and three glasshouse experiments using lateritic soils from south-western Australia. Non-reactive Queensland rock phosphate (low carbonate-substituted apatite from the Duchess deposit) was also used in the pot experiments. Bicarbonate-soluble phosphorus extracted from the soil is widely used in Western Australia to predict plant yields from previously-applied fertilizer dressings. For both field and pot experiments bicarbonate-extractable phosphorus (soil test value) was measured and related to subsequent plant yields.As calculated from the initial slope of the relationship between yield and the level of P applied, finely powdered NCRP was about 5–32% as effective as freshly-applied superphosphate in the year of application and also for two years after application in the field experiment, and for two successive crops in the three pot experiments. For both field and pot experiments, finely powdered NCRP, was at best, 1.5–2.0 times as effective as granular NCRP. Relative to freshly-applied superphosphate, the effectiveness of rock phosphates usually decreased with increasing level of application.For each of the crops in the field experiment, the relationships between yield and phosphorus content of plants (i.e. internal efficiency curves) were similar for all fertilizers. Thus the low effectiveness of the rock phosphates relative to superphosphate was solely due to much less phosphorus being taken up by plants. By contrast, in the pot experiments internal efficiency curves differed for different fertilizers. This is attributed to differences in the rate of phosphorus uptake by plant roots during the early stages of plant growth.For both field and pot experiments, soil test calibrations (the relationship between yield and soil test value) differed for rock phosphates and superphosphate. For superphosphate, soil test calibrations also differed for the three different years after the initial application of this fertilizer in the field experiment. For the second crop in the pot experiment, soil test calibrations differed for superphosphate applied at different times (before the first and the second crop). These results point out the difficulty of applying soil testing procedures to soils that have experienced different histories of fertilizer application.     

Induced phosphorus fixation and the effectiveness of phosphate fertilizers derived from Sukulu Hills phosphate rock

A greenhouse study was conducted with two surface, acidic soils (a Hiwassee loam and a Marvyn loamy sand) to measure the effect of increasing P-fixation capacity, on the relative agronomic effectiveness (RAE) of phosphate fertilizers derived from Sukulu Hills phosphate rock (PR) from Uganda. Prior to fertilizer application, Fe-gel was added to increase P-fixation capacity from 4.4 to 14.3% for the Marvyn soil and from 37.0 to 61.5% for the Hiwassee soil. Phosphate materials included compacted Sukulu Hills concentrate PR + Triple superphosphate (CTSP) at a total P ratio of PR:TSP = 50:50; 50% partially acidulated PR (CPAPR) from Sukulu Hills concentrate PR made with H₂SO₄; and Sukulu Hills concentrate PR (PRC) made by magnetically removing iron oxide from raw PR ore. Triple superphosphate (TSP) was used as a reference fertilizer. After adjusting soil pH to approximately 6, P sources were applied at rates of 0, 50, 150, and 300 mg total P kg^–1 soil. Two successive crops of 5 week old corn seedlings (Zea mays L.) were grown. The results show that the RAE of the phosphate materials measured using dry-matter yield or P uptake generally decreased as P-fixation capacity was increased for both soils. CTSP was more effective in increasing dry-matter yield and P uptake than CPAPR. PRC alone was an ineffective P source. Soil chemical analysis showed that Bray 1 and Mehlich 1 extractants were ineffective on the high P-fixation capacity Fe-gel amended Hiwassee soil. Mehlich 1 was unsuitable for soils treated with PRC since it apparently solubilizes unreactive PR. When all of the soils and P sources were considered together, Pi paper was the most reliable test for estimating plant available P.     

碳基固体酸催化纤维素热解制备左旋葡聚糖和左旋葡萄糖酮

将纤维素快速热解转化为高价值的左旋葡聚糖和左旋葡萄糖酮是国内外研究热点之一。通过制备及表征碳基固体酸,并优化纤维素催化热解的实验条件,在350℃下,Fe₃O₄/C₇₀₀-H₃PO₄与纤维素以1∶3的比例混合,可以显著提高热解过程中左旋葡聚糖[40.7%（质量）]和左旋葡萄糖酮[13.5%（质量）]的产率,分别比纯纤维素热解提高了2倍和22倍。该研究对纤维素的定向高值化转化具有指导意义。     

The role of soil pH in the dissolution of phosphate rock fertilizers

The influence of soil pH on the dissolution of phosphate rock fertilizers was investigated in laboratory experiments with reactive North Carolina phosphate rock (PR) in a lateritic soil adjusted to several pH values. Increased soil pH resulted in decreased dissolution as estimated by the increase in exchangeable calcium (Ca) method. The extent of PR dissolution was related to soil pH by an equation of the form Log Ca = a–b pH, and it increased with contact period and rate of PR application. Increased plant available P, as estimated by NaHCO₃ soluble-P (BicP) was about one third of the P dissolved from PR. BicP was related to soil pH by an equation of the form Log Bic P = c–d pH. Dissolution of PR in soil can be considered as a simple chemical reaction between apatite and hydrogen ions supplied by soil constituents.     

盐酸浸取磷矿石的研究

对工业级盐酸浸取磷矿石进行了研究。利用3因素二次回归法设计了一个零水平的正交实验,得到了盐酸浸取磷矿石的数学模型。此模型可预测盐酸质量分数、实际盐酸用量与理论用量比、反应时间等3种因素对磷矿石中五氧化二磷浸取率的影响。同时得出最佳反应条件：盐酸质量分数26％,实际盐酸用量为理论用量的105％,反应时间1．5h。此时磷矿的五氧化二磷浸取率可以达到98．45％。     

Phosphorus availability from partial acidulation of two phosphate rocks

Two phosphate rocks, one from Pesca (Colombia) and the other from Togo, were acidulated to various degrees with H₂SO₄ and H₃PO₄ for evaluation in varying granule size ranges. Products acidulated with H₂SO₄ were also prepared using different drying temperatures. Phosphorus availability was measured by dry-matter yield and P uptake in greenhouse experiments with maize.It was observed that partial acidulation with H₂SO₄ was effective in increasing the water-soluble P level of phosphate rock when the drying temperature of the product was not excessive. Crop response and P uptake were both highly correlated to the water solubility of the product. The relative agronomic effectiveness (RAE) of Togo rock increased from 3% when unacidulated to 33%, 47%, and 52% when 20%, 30%, and 40%, respectively, of the H₂SO₄ required to make SSP was added. Similar results were obtained with Pesca rock. No consistent effect due to granule size was observed.Twenty percent acidulation of Pesca rock with H₃PO₄ was 53–76% as effective as TSP with a single crop and 79–90% as effective over three cropping periods, showing a potential for high residual value.     

Summary of research on soil testing for rock phosphate fertilizers in Western Australia

The relationship between plant yield and values of soils tests for phosphorus (P) was studied in long-term field experiments in south-western Australia for soil previously fertilized with rock phosphate and superphosphate. The rock phosphates studied were: Queensland (Duchess) apatite rock phosphate; reactive apatite rock phosphate from North Carolina; and rock phosphate from Christmas Island (as either C-grade ore or Calciphos). The P fertilizers were applied once only at the start of each experiment, and in subsequent years, soil samples were collected in January-March to measure soil test values. These were compared with plant yields measured later on in that year. The Colwell alkaline bicarbonate soil test was used in all years in all experiments. Olsen, Bray, lactate and Troug tests were used in some years in some experiments. For all soil tests the relationships between yield and soil test values was generally different for rock phosphate and superphosphate. For a given source of P, none of the different soil test reagents was significantly superior for predicting plant yields. The relationship between yield and soil test value was also generally different for different plant species. At one site cultivation was included as a treatment and the relationship varied depending on the cultivation treatment of the topsoil before sowing oats (Avena sativa). The relationship between yield and soil test also differed between years.     

The hydrochloric acid route for phosphate rock

When phosphate rock is leached with hydrochloric acid, radium can be removed by co-precipitation with Ba_0.4Ca_0.6SO₄ and uranium by extraction with a 5% solution of tributyl phosphate in hexane or Varsol. Phosphoric acid is then separated from calcium chloride solution and other impurities by extraction with undiluted tributyl phosphate. The lanthanides can be precipitated from the raffinate by NH₃, and CaSO₄.2H₂O by H₂SO₄ to regenerate HCl for recycle. The organic phase containing H₃PO₄ can be stripped by NH₃ to yield ammonium phosphate and to regenerate the tributyl phosphate for recycle. Fluorine can be precipitated from the initial leach solution as Na₂SiF₆.