Agronomic efficiency of phosphate fertilizers produced by the re-use of a metallurgical acid residue

Abstract

The production of fertilizers with industrial wastes reduces the environmental impacts of waste disposal and improves environmental sustainability by generating added-value products. Our objective with this study was to evaluate the agronomic performance and potential soil/plant contamination with heavy metals of alternative phosphate (P) fertilizers, obtained from the acidulation of phosphate rocks (PR) by a metallurgical acidic waste. Seven P fertilizers were evaluated: three PR (Araxá, Patos, and Bayóvar), their respective acidulated products (PAPR), and triple superphosphate fertilizer (TSP). A greenhouse trial was carried out to test the agronomic performances of fertilizers in a sequentially cultivated maize-soybean-white oat. The reaction of PR with acid waste was effective to increase their solubility and improve plant yield and P uptake compared to their natural PR. There was a cumulative recovery by plants of 1.4 and 8.1% of added P via PR and PAPR, respectively. No increase in heavy metal (Cd, Pb, Cr, and Ni) availability in soil or accumulation in shoots was observed, indicating that the PAPR were environmentally safe. The usage of acid waste to produce P fertilizers therefore represents a strategic way to employ marginal products for the production of fertilizers.

Acid Ammonium Citrate as P Extractor for Fertilizers of Varying Solubility

“…For P extractability in all used extractors, the acid treatment of Araxá and Patos PRs showed to be effective in increasing the fertilizer quality of their end products (PAPR), especially for water-P, CNA-P, and CA-P (Mattiello et al, 2016;Santos et al, 2016;Barreto et al, 2018), but also for FA_P and AAC_P. This increase in the solubility of PAPR products was due to the transformation of apatite minerals into new P species, supposedly non-crystalline iron and calcium phosphate as well as monocalcium phosphate and dicalcium phosphate, as reported by Santos et al (2016).…”

“…Araxá PR is an apatite concentrate from igneous deposits, while Patos PR is obtained from a sedimentary medium-grade metamorphism Rev Bras Cienc Solo 2019;43:e0180072 deposit; both can be found in the state of Minas Gerais, Brazil. The highly crystalline hydroxyapatites and fluorapatites are the most common P sources in Brazilian phosphates (Santos et al, 2016), considered to be low-reactive fertilizers for direct use (Barreto et al, 2018). In addition, the high occurrence of Fe-, Al-, and Si species in the deposits of these phosphates has prompted the industries to concentrate the apatite minerals prior to the production of P-fertilizers.…”

“…Partially acidulated phosphate rocks (PAPRs) are produced by reaction of PRs with an acidic wastewater, as demonstrated by Barreto et al (2018). The wastewater is highly acidic (pH ~ 0 and 5.75 mol L -1 H + ), with high concentrations of some plant nutrients, such as S-SO 4 2-(791 g L -1 ), N-NO 3 -(18 g L -1 ), Cl-Cl -(128 g L -1 ), P-PO 4 3-(19 g L -1 ), Fe (13,595 mg L -1 ), K (3,438 mg L -1 ), and Mn (1,199 mg L -1 ) (Santos et al, 2016).…”

“…Eight samples of phosphate fertilizers of distinct solubility were evaluated in a greenhouse test with corn (Barreto et al, 2018); we investigated the consistencies of different methods to extract P of fertilizers and their correlations with plant uptake and dry matter production.…”

“…Soluble P in ammonium citrate, pH 3 (AAC-P) and 2 % formic acid (FA-P), were measured following Chien and Hammond (1978) and Braithwaite et al (1989), respectively. Total P-P 2 O 5 , water-P, and NAC-P data, except for SSP fertilizers, were compiled from Barreto et al (2018). DMP = dry matter production; P uptake in the control treatment (no P applied) were 1.1 ± 0.1 g pot -1 and 0.6 ± 0.1 g pot -1 , respectively.…”