The invention discloses a production method of a slow-release chelated compound
fertilizer containing multiple elements. The method comprises the following steps of: preparing a
humic acid solution and concentrated
sulfuric acid into a
humic acid-
sulfuric acid mixed solution of 70-90 DEG C; spraying into a rotor drum granulator for granulating together with other powdery basic fertilizers containing
nitrogen,
phosphorus and
potassium, substances which are rich in medium and trace elements, nutrients which can be adsorbed and fixed, and ingredients which can be used for forming a
coating framework and an
inner membrane shell; after granulating, enveloping with liquid
sodium silicate, and
drying, cooling, sieving and packing to obtain a
nitrogen-
phosphorus-
potassium slow-release chelated compound
fertilizer containing organic matters and medium and trace elements such as
sulfur,
zinc,
calcium,
magnesium and
silicon. The liquid
sodium silicate serving as an enveloping material is added in two parts, one part is directly added into the material layer of the rotor drum granulator to increase the granulating rate and form the
inner membrane shell with the
viscosity, and the other part is added into the outlet of the rotor drum granulator to envelop the surfaces of granulated
fertilizer particles. The processes of material
granulation and fertilizer particle enveloping are completed by using the rotor drum granulator, and curing treatment of a membrane body is completed by
drying and cooling without adding any special enveloping equipment, so that a large quantity of equipment investments are reduced.